DEE 


ELECmO-TECiiHICAL 
SERIES 


BY  THE  SAME  AUTHORS 

Elementary  Electro  -  Technical  Series 

COMPRISING 

Alternating  Electric  Currents. 
Electric  Heating. 

Electro-magnetism. 

Electricity  in  Electro-Therapeutics. 

Electric  Arc  Lighting. 
Electric  Incandescent  Lighting. 
Electric  Motors. 

Electric  Street  Railways. 
Electric  Telephony. 

Electric  Telegraphy. 

Cloth,       Price  per  Volume,        $1.00. 


Electro-Dynamic  Machinery. 
Cloth,  $2.50. 


THE  W.  J.  JOHNSTON  COMPANY 

253  BROADWAY,  NEW  YORK 


ELEMENTARY  ELECTRO-TECHNICAL   SERIES 


THE  ELECTRIC  MOTOR 


AND    THE 


TRANSMISSION  OF  PO¥ER 


BY 

EDWIN  J.  HOUSTON,  PH.  D. 

AND 

A.  E.  KENNELLY,  Sc.  D. 


NEW  YORK 

THE  W.  J.  JOHNSTON  COMPANY 

253  BROADWAY 

1896 


COPYRIGHT,  1896,  BY 
THE  W.  J.  JOHNSTON  COMPANY. 


PREFACE. 


THERE  is  probably  no  subject,  con- 
nected with  the  application  of  electricity, 
that  has  come  into  greater  prominence 
during  the  last  decade,  than  the  electric 
transmission  of  power.  The  electric 
motor  is  now  to  be  found  everywhere 
driving  machinery  of  all  sizes.  It  permits 
a  single,  large,  economical*  engine  to  oper- 
ate a  number  of  small  motors  over  a  large 
area. 

This  little  volume  of  the  Electro- Tech- 
nical Series  has  been  prepared  with  the 
object  of  rendering  the  principles  of  elec- 
tric motors  clear  to  those  who  are  not 
specially  trained  in  electro-technics.  For 


M289307 


IV  PREFACE. 

this  reason,  in  this,  as  in  all  other  books  of 
the  series,  vexed  questions  as  regards  the 
priority  of  invention  have  been  carefully 
avoided,  and  facts,  rather  than  names,  have 
been  presented  to  the  reader.  Only  such 
portions  of  the  history  of  the  subject  as  are 
necessary^to  a  logical  comprehension  of  its 
development  are  given,  and  no  mathe- 
matical treatment  other  than  simple  arith- 
metic has  been  employed. 

The  authors  are  indebted  to  the  editors 
of  Cassie^s  Magazine  for  cuts  in  the  book 
relating  to  the  Niagara  power  transmission. 

Notwithstanding  the  apparent  complex- 
ity of  the  electric  motor,  the  authors 
believe  that  the  student  will  be  in  pos- 
session of  all  its  essential  elementary 
principles  after  reading  this  book. 

AUGUST,  1896. 


CONTENTS. 


I.  INTRODUCTORY,   .                 .        .        .  1 
II.  SOURCES  OF  ENERGY,          .         .         .19 

III.  ELEMENTARY  ELECTRICAL  PRINCIPLES,  29 

IV.  EARLY  HISTORY  OF  THE  ELECTROMAG- 

NETIC MOTOR,          ....  73 

V.  ELEMENTARY  THEORY  OF  THE  MOTOR,  119 
VI.  STRUCTURE   AND    CLASSIFICATION   OF 

MOTORS, 162 

VII.  INSTALLATION    AND     OPERATION     OF 

MOTORS, 200 

VIII.  ELECTRIC  TRANSMISSION  OF  POWER,   .  217 

IX.  ALTERNATING-CURRENT  MOTORS,        .  241 


VI  CONTENTS. 

CHAPTER  PAGE 

X.  ROTATING  MAGNETIC  FIELDS,      .  .;;     284 
XL  ALTERNATING-CURRENT       TRANSMIS- 
SIONS,     ..  :j  ,;*,.. '.. ..,     '•  ,.        ,  .     302 
XII.  MISCELLANEOUS      APPLICATIONS  OF 

ELECTRIC     MOTORS,        .       . .  .     335 

INDEX,            .         .         .  •      .         .         -?  »     359 


THE    ELECTRIC    MOTOR   AND 

THE  TRANSMISSION  OF 

POWER. 


CHAPTER  I. 

INTKODUCTOKY. 

THE  nineteenth  century  owes  its  promi- 
nence in  physical  science,  largely  to  the 
discovery  that  energy  is  indestructible,  and 
that  the  universe  possesses  a  certain  stock 
or  store  of  energy  which  it  is  impossible 
either  to  increase  or  to  decrease. 

All  natural  phenomena  are  attended 
by  transformations  of  energy.  When 


2  THE   ELECTRIC    MOTOR   AND 

energy  disappears  in  one  form,  the  nine- 
teen tli  century  doctrine  of  the  conservation 
of  energy,  bids  us  look  for  some  other 
form  in  which  we  know  it  must  reappear. 
The  fact  that  phenomena  occur  at  one 
point  of  space  where  the  energy  necessary 
for  this  causation  did  not  previously  exist, 
proves  that  energy  must  have  been  taken 
from  some  store  or  stock  and  transmitted 
to  that  point.  Consequently,  the  doctrine 
of  the  conservation  of  energy  necessitates 
the  doctrine  of  the  transference  or  trans- 
mission of  energy,  in  contradistinction  to 
its  creation.  In  other  words,  the  discov- 
ery of  the  indestructibility  of  energy  was 
also  the  discovery  of  the  possibility  of  its 
transmission. 

The  discovery  of  the  doctrine  of  the  in- 
destructibility and  increatability  of  energy 
followed  upon  the  discovery  of  the  in- 


THE  TRANSMISSION   OF   POWER. 

destructibility  and  increatability  of  matter. 
Our  belief  in  these  doctrines  is  the  result 
of  our  universal  experience,  and  any  ex- 
planation of  natural  phenomena,  that  neces- 
sitates the  creation,  either  of  energy  or  of 
matter,  may  be  unhesitatingly  rejected. 

Energy  is  the  capability  of  doing  work. 
In  other  words,  when  work  is  done  energy 
is  expended.  But  it  must  not  be  supposed 
because  the  energy  is  expended,  that  it  is 
thereby  destroyed.  The  energy  has  only 
changed  its  form  or  its  position.  For 
example,  when  a  charge  of  gunpowder  is 
placed  in  a  gun  and  fired,  the  energy 
which  previously  existed  in  the  gun- 
powder is  liberated,  by  the  act  of  firing, 
and  is  principally  expended  in  moving 
the  ball  from  the  gun,  some  being  acci- 
dentally expended  in  heating  the  gun. 
Although  the  energy  is  thus  properly 


4  THE   ELECTRIC   MOTOR   AND 

spoken  of  as  being  expended  by  the  gun- 
powder in  doing  this  work,  yet  it  must  be 
remembered  that  the  energy  is  not  there- 
by annihilated,  but  is  merely  transformed. 
The  moving  ball  expends  some  of  its 
energy  of  motion  in  moving  aside  the  air ; 
a  part  is  expended  in  producing  sound,  and 
the  remainder,  usually  the  greater  part,  is 
given  up  in  the  concussion  against  the 
body  it  strikes.  All  this  energy  finally 
takes  the  form  of  heat  in  the  gun,  in  the 
air,  and  in  the  body  struck,  in  which  form 
it  usually  permanently  remains.  Conse- 
quently, after- the  gun  has  been  fired,  there 
is  less  chemical,  but  more  heat  energy  in 
that  part  of  the  universe. 

As  another  example  take  the  case  of  a 
reservoir  filled  by  a  pump  with  water.  The 
filled  reservoir  represents  a  stock  or  store 
of  energy  derived  from  the  work  expended 


THE   TRANSMISSION    OF   POWER.  5 

in  pumping.  So  long  as  no  water  is 
allowed  to  leave  the  reservoir,  no  work  is 
done,  and  the  store  of  energy  remains  un- 
changed. If,  however,  the  water  be  per- 
mitted to  escape  through  a  water-wheel, 
the  energy  in  the  reservoir  is  expended  in 
turning  the  wheel ;  that  is  to  say,  the 
energy  of  the  moving  water  is  transferred 
to  the  moving  wheel,  which  in  its  turn, 
may  transfer  it  to  machinery  connected 
therewith.  Here  each  moving  part  ex- 
pends its  energy ;  but  such  energy  is  not 
annihilated;  it  is  merely  transferred.  If 
the  water-wheel  were  employed  to  drive 
another  pump  which  filled  a  similar  reser- 
voir to  the  same  level,  and  no  loss  of 
energy  occurred  in  its  transference,  the 
escape  of  water  from  the  first  reservoir 
would  result  in  the  filling  of  the  second 
reservoir  with  the  same  quantity  of  water 
and  to  the  same  depth.  In  practice,  this 


6  THE   ELECTEIG    MOTOR   AND 

never  occurs;  losses  always  take  place  in 
the  machinery.  Such  losses,  however,  are 
not  annihilations  of  energy.  The  energy 
which  disappears,  takes  some  other  form, 
generally  as  heat  produced  by  frictions. 

The  water  of  a  river  flowing  through  its 
channel,  represents  a  stock  of  energy  that 
is  being  expended  at  a  certain  rate.  The 
amount  of  energy  present  in  the  moving 
stream  depends  both  upon  the  quantity 
of  water,  and  on  the  speed  with  which 
it  moves.  A  certain  proportion  of  this 
energy  is  capable  of  being  transferred 
from  the  stream  to  a  moving  water-wheel, 
or  water  motor,  and  the  water,  which  has 
passed  through  the  wheel  or  motor,  loses 
some  of  its  motion  in  consequence. 

The  source  of  energy  in  the  moving 
water  of  a  river  is  to  be  found  in  the  sun's 


heat,  wlvd*  conv 

1L\       /O 

into  vapor^^^arried  this 
land,  where  i^>^^ecj[j^ii3^  -boadeil sed  and 
fell  as  rain.  The  energy  in  the  moving 
water,  however,  is  only  a  portion  of  that 
which  it  acquired  in  falling  from  the 
higher  to  the  lower  level. 

In  each  of  the  preceding  cases  the  mov- 
ing machinery  ceased  its  motion,  when 
energy  ceased  to  be  transferred  to  it ;  and, 
in  each  case,  we  have  been  able  readily 
to  trace  the  source  of  the  driving  energy. 
The  case  of  a  man,  who  expends  muscular 
or  nervous  energy,  in  doing  work,  forms  no 
exception  to  this  rule.  In  order  to  permit 
the  man  to  continue  expending  energy  in 
such  work,  it  is  necessary  that  his  stock  of 
energy  be  replenished  from  time  to  time ; 
in  other  words,  that  energy  be  transferred 
to  him  from  some  other  source.  This  is 


8  THE   ELECTRIC   MOTOR  AND 

accomplished  by  his  assimilating  food, 
which  contains  chemical  energy  imparted 
to  it  from  the  sun. 

Strange  as  it  may  seem,  the  transference 
of  energy  from  assimilated  food  to  the 
organism  of  the  man,  is  similar  to  the 
transference  of  energy  from  a  lump  of 
coal  to  a  steam  engine.  The  chemical 
potential  energy  of  the  coal,  liberated 
by  burning  under  a  boiler,  is  transferred 
to  the  steam  ;  and  the  energy  of  the  steam, 
is  transferred  to  the  working  parts  of  the 
steam  engine.  In  man,  it  is  the  chemical 
potential  energy  of  the  food  assimilated, 
which  enables  him  to  perform  his  varied 
functions.  In  the  steam  engine  it  is  the 
chemical  potential  energy  of  the  coal  which 
enables  it  to  work. 

Before  leaving  the  subject  of  energy  it 


THE   TRANSMISSION   OF   POWER.  9 

will  be  advisable  to  obtain  definite  ideas 
concerning  its  measurement.  The  amount 
of  energy  required  to  be  expended  in  order 
to  raise  one  pound  against  the  earth's 
gravitational  force,  through  a  vertical  dis- 
tance of  one  foot,  is  called  a  foot-pound. 
Thus,  to  raise  a  steel  fire-proof  safe, 
weighing  5,000  pounds,  from  the  street 
to  a  room,  100  feet  above  the  street  level, 
requires  the  expenditure  of  energy  equal 
to  100  x  5,000  =  500,000  foot-pounds. 
Energy  is  measurable  in  units  of  work, 
and  the  foot-pound  is  the  unit  frequently 
employed  in  English-speaking  countries 
for  this  purpose. 

The  international  unit  of  work  is  called 
the  joule.  A  joule  is  approximately  0.738 
foot-pound,  and  is,  therefore,  roughly, 
equal  to  the  amount  of  energy  required  to 
be  expended  in  order  to  raise  a  pound 


10  THE   ELECTRIC   MOTOR   AND 

through  a  distance  of  9",  against  gravita- 
tional force.  A  foot-pound,  is,  therefore, 
greater  than  a  joule,  being,  approximately, 
equal  to  1.355  joules. 

If  we  could  compute  the  total  energy  of 
the  universe,  it  would,  of  course,  be  capable 
of  being  expressed  either  in  foot-pounds  or 
in  joules.  As  we  have  already  stated  this 
total  is  believed  to  be  constant,  all  so- 
called  expenditures  of  energy  merely 
altering  the  character  of  the  stock,  and  not 
its  amount. 

It  is  necessary  carefully  to  distinguish 
between  the  expenditure  of  energy  and 
the  rate  at  which  it  is  expended.  Thus  if 
a  man  weighing  150  pounds  ascends  a 
flight  of  stairs  100  feet  high,  he  must 
necessarily  expend  energy  amounting  to 
150X100  =  15,000  foot-pounds.  So  far 


THE  TRANSMISSION   OF  POWER.  11 

as  the  result  is  concerned,  namely  his 
reaching  the  top  of  the  stairs,  the  same 
amount  of  work  must  be  done  whether  he 
does  this  in  five  minutes,  or  in  one 
minute  ;  but  the  rate  at  which  he  requires 
to  expend  energy  in  the  two  cases  in  order 
to  mount  the  stairs,  would  be  very  differ- 
ent ;  for,  in  the  first  case  he  would  expend 
15,000  foot-pounds  of  work  in  five 
minutes,  or  at  an  average  rate  of  3,000 
foot-pounds  per  minute,  while  in  the 
second  case  he  would  expend  15,000  foot- 
pounds of  work  in  one  minute,  or  at  an 
average  rate  of  15,000  foot-pounds  per 
minute ;  that  is  to  say,  his  activity,  or  rate- 
of-expending-energy,  would  be  five  times 
greater  in  the  latter  case  than  in  the 
former. 

A  unit  of  activity  or  rate-of-expending- 
energy,   frequently    adopted    in    English- 


12  THE   ELECTEIC   MOTOR  .AND 

speaking  countries,  is  the  foot-pound-per- 
second.  A  similar  unit  employed  in  deal- 
ing with  machinery  is  called  the  Jiorse- 
power  and  is  equal  to  550  foot-pounds-per- 
second. 

The  international  unit  of  activity  is  the 
joule-per -second  /  or,  as  it  is  more  fre- 
quently called,  the  watt.  Expressed  in 
foot-pounds-per-second,  the  watt  is  0.738 
foot-pound-per-second,  so  that  746  watts 
are  equal  to  one  horse-power.  As  the 
watt  is  usually  too  small  a  unit  for  con- 
veniently dealing  with  machinery,  the 
kilowatt  or  1,000  watts,  is  generally  em- 
ployed. One  kilowatt  (KW),  is,  approxi- 
mately, 1  1/3  horse-power  (1.34  HP),  i.  e. 
746  watts  =  1  HP. 

As  we  have  seen,  natural  phenomena 
require  an  expenditure  of  energy  to  pro- 


THE  TRANSMISSION  OF  POWER.  13 

duce  them.  It  is  convenient  to  regard 
such  phenomena  either  from  the  stand- 
point of  the  energy  they  consume,  or  of 
the  activity  they  require  to  have  sus- 
tained. 

We  can  regard  these  phenomena  as 
capable  of  being  reproduced  by  the  expen- 
diture of  the  proper  amount  of  energy. 
Since  the  chemical  potential  energy  in  a 
pound  of  coal  is  a  definite  quantity,  we 
know  that  by  the  liberation  of  this  energy 
we  can  produce  a  certain  phenomenon, 
such,  for  example,  as  raising  a  weight  to 
a  given  height,  or  in  overcoming  certain 
resistances,  as  in  sawing  a  log  of  wood. 
If  the  same  phenomenon  is  to  be  produced 
at  some  point  where  this  energy  does  not 
exist,  it  is  evident  that  this  amount  of 
energy  must  be  transmitted  from  some 
other  point. 


14  THE  ELECTRIC   MOTOR  AND 

In  mills  and  manufactories,  where  dif- 
ferent machines  are  to  be  driven,  it  is  pos- 
sible to  determine  the  exact  amount  of 
energy  required  to  drive  them.  We  can, 
therefore,  calculate  the  amount  of  steam 
power  or  water-power  required  to  be  sup- 
plied to  such  establishments.  In  actual 
practice,  the  problem  presented  is  the 
determination  of  the  most  effectual  and 
economical  means  whereby  this  amount  of 
power  may  be  transmitted  from  the  point 
of  supply  to  the  point  of  delivery,  where 
the  machine  has  to  be  driven. 

Various  means  have  been  adopted  for 
the  transmission  of  power  to  considerable 
distances.  The  principal  of  these  are  : 

(1)  Rope  transmission. 

(2)  Pneumatic  transmission. 

(3)  Hydraulic  transmission. 

(4)  Electric  transmission. 


THE  TRANSMISSION   OF  POWER.  15 

Rope  transmission  finds  its  most  exten- 
sive use  in  the  operation  of  cable  cars, 
where  it  is  sometimes  employed  for  dis- 
tances of  several  miles  in  a  single  section. 

Pneumatic  transmission  is  employed  ex- 
tensively in  Paris,  where  there  are  about 
35  miles  of  pneumatic  mains.  It  is  also 
used  extensively  in  mining  operations, 
and  to  some  extent,  in  systems  of  railway 
signalling.  When  used  in  mining,  it 
possesses  the  advantage  of  aiding  the 
ventilation. 

Hydraulic  transmission  is  in  fairly 
extensive  use  for  distributing  power  in 
European  cities  where  the  distribution 
distances  are  not  excessive. 

There  can  be  no  doubt  that  any  of  the 
preceding  systems  is  capable,  when  prop- 


16  THE  ELECTRIC   MOTOR  AND 

erly  installed,  of  transmitting  power  with 
fair  economy  over  considerable  distances. 
A  transmission  system  consists  of  gener- 
ators at  the  transmitting  end,  which  trans- 
form the  energy  supplied  into  a  form  in 
which  it  can  be  transmitted ;  motors,  or 
devices  at  the  receiving  end,  for  transform- 
ing the  energy  so  transmitted  into  the 
form  available  for  use;  and  connecting 
systems  joining  the  generators  and  motors. 
In  considering  the  relative  advantages  of 
any  transmission  system,  it  is  evident  that 
account  must  be  taken  of  the  cost  of  instal-" 
lation  of  the  entire  system,  and  of  the  rela- 
tive efficiencies  of  the  generators  and 
motors ;  or,  combining  these  things,  of  the 
cost  of  delivering  power.  In  addition 
to  this  we  must  consider  the  readiness 
with  which  the  transmitted  power  can  be 
transformed,  and  the  safety  with  which  it 
can  be  both  transmitted  and  employed. 


THE   TRANSMISSION    OF   POWER.  17 

111  contrasting  the  relative  advantages  of 
rope,  pneumatic,  and  hydraulic  transmis- 
sion, rope  transmission  is  often  advanta- 
geous where  the  power  has  to  be 
transmitted  in  the  open  country  in  bulk, 
but,  where  power  has  to  be  transmitted  to 
a  number  of  consumers  in  a  city,  pneu- 
matic or  hydraulic  transmission  possess 
advantages  over  rope  transmission,  espe- 
cially in  cases  where  the  exigencies  of 
the  work  require  the  direction  of  the 
motion  to  be  frequently  and  abruptly 
changed. 

While  pneumatic  and  hydraulic  trans- 
mission systems  possess  marked  advantages 
in  certain  directions,  yet  electric  transmis- 
sion is  so  convenient,  the  efficiency  of  the 
generators  and  motors  so  high,  the  cost  of 
transmission  over  considerable  distances  so 
comparatively  low,  and  the  flexibility  with 


18  ME  ELECTRIC  MOTOK. 

which  electricity  lends  itself  to  the  purposes 
of  general  distribution  so  marked,  that 
electricity  is  already  in  extensive  use  in 
the  United  States  for  the  transmission  of 
power. 


PROPERTY  CF' 


SOURCES    OF    ENERGY. 

THE  known  sources  of  energy  may  be 
classified  as  follows  :  viz., 

(1)  Chemical   energy,   as  of    coal    and 
other  combustibles. 

(2)  Water  power. 

(3)  The  earth's  internal  heat. 

(4)  The  earth's  motion. 

(5)  Solar  heat. 

Tracing  these  various  sources  of  energy 
to  their  origin,  it  soon  becomes  evident 
that  they  are  all  derived  from  the  sun  as 
the  prime  source.  A  lump  of  coal,  when 
burned,  gives  out,  in  its  radiant  light 


19 


20  THE   ELECTRIC   MOTOK  AND 

and  heat,  the  solar  activity  of  a  past  geo- 
logical age.  So  also  the  energy  of  food, 
which  when  assimilated,  is  the  source  of 
energy  in  the  muscles  of  animals,  has 
been  derived  from  the  sun  in  more  recent 
times.  Wind  power  and  water  power  also 
manifestly  derive  their  energy  from  the 
sun. 

* 

The  earth's  heat  is  properly  to  be  re- 
garded as  a  source  of  power.  Since  the 
entire  interior  of  the  earth  is  believed  to 
be  highly  heated,  we  evidently  .have  in  it  a 
great  storehouse  of  natural  power,  which 
although  never  yet  practically  employed, 
yet  is  capable  of  doing  an  enormous  amount 
of  work.  Since  it  is  generally  believed,  in 
accordance  with  Laplace's  nebular  hypo- 
thesis, that  the  earth  and  all  members  of 
the  solar  system  once  formed  a  part  of  the 
sun,  and  were  disengaged  from  the  sun's 


THE  TRANSMISSION   OF   POWER.  21 

mass  while  in  an  incandescent  condition, 
this  source  of  heat  also  owes  its  origin 
to  the  sun. 

The  rotary  motion  of  the  earth  may 
be  regarded  as  a  source  of  power.  With- 
out stopping  to  discuss  the  various  methods 
which  have  been  proposed  to  obtain  motion 
from  the  rotation  of  the  earth,  we  would 
point  out  that  the  only  practical  means 
for  doing  this  is  by  the  employment  of 
machines  driven  by  the  tides. 

It  is  evident,  from  a  consideration  of 
the  above,  that  all  the  natural  sources 
of  power  available  to  man  on  the  earth 
either  have  been,  or  are  being,  derived 
from  the  sun,  and  are  divisible  into  three 
great  classes ;  namely, 

(1)  Solar  energy  imparted  to  the  earth 
at  the  beginning  of  its  career. 


22  THE  ELECTRIC   MOTOR   AND 

(2)  Solar  energy  imparted  to  coal  dur- 
ing past  geological  epochs ;  and, 

(3)  Solar  energy  imparted  to  the  earth 
at  the  present  time  by  direct  radiation. 

Although,  as  we  have  already  seen,  the 
total  amount  of  energy  existing  in  the  uni- 
verse is  believed  to  be  constant,  yet  the 
amount  residing  in  the  sun  and  in  the 
earth,  is  believed  to  be  steadily  diminish- 
ing, being  lost  by  radiation  into  interstellar 
space  at  a  comparatively  rapid  rate. 

A  motor  which  receives  power  and 
transmits  it  to  the  machinery  it  drives 
is  a  device  for  transforming  or  trans- 
ferring energy.  A  certain  amount  of 
energy  must  be  expended  in  driving  it ;  that 
is  a  certain  amount  of  activity  must  be 
delivered  to  the  machine.  This  activity 
is  generally  known  as  the  intake  of  the 


THE  TRANSMISSION   OF   POWER.  23 

machine.  The  machine,  in  operating,  de- 
livers to  the  machinery  it  drives  a  certain 
amount  of  activity  which  is  called  its  out- 
put. The  output  can  never  exceed  the  in- 
take. In  point  of  fact,  since  certain  losses 
occur  in  the  operation  of  the  best  designed 
machines,  the  output  can  never  even  equal 
the  intake,  and,  in  many  machines,  is  con- 
siderably less  than  the  intake.  The  ratio 
of  the  output  to  the  intake  is  called  the 
efficiency  of  the  machine. 

In  order  to  illustrate  the  preceding 
principles  we  may  consider  the  following 
example.  A  line  of  shafting  in  a  machine 
shop,  is  a  machine  for  transferring  energy 
from  a  source,  say  a  steam  engine,  to  one 
or  more  driven  machines,  such  as  lathes, 
saws,  etc.  The  amount  of  activity  de- 
livered to  the  shafting  by  the  engine  may 
be,  say  10  horse-power,  or  746  x  10  =  7,460 


24  THE   ELECTRIC   MOTOR   AND 

watts  =  7,460  joules-per-second,  or  5,500 
foot-pounds  per  second.  A  certain  amount 
of  this  activity  is  expended  in  overcoming 
the  friction  of  the  shafting;  i.  e.,  in  heat- 
ing the  journals,  in  churning  the  neigh- 
boring air,  in  shaking  the  building,  and  in 
stretching  the  belts.  The  remainder  of 
the  activity  is  delivered  to  the  lathes.  If 
this  total  delivery  or  output,  be  8  HP  = 
746  X  8  =  5,968  watts,  the  efficiency 

of  the  shafting  will  be  —  =  80  per  cent. 

Again  if  an  electric  motor  receives  an 
intake  of  50  horse-power,  and  has  an  out- 
put of  45  horse-power;  i.  e.,  delivers  45 
horse-power  at  its  pulley,  then  its  efficiency 

will  be  —  =  0.9  =  90  per  cent. 

In   considering   the   amount   of    power 


THE   TRANSMISSION   OF   POWER.  25 

required  to  be  drawn  from  any  natural 
source  in  order  to  perform  a  given  amount 
of  work,  allowance  must,  therefore,  be  made 
for  the  loss  in  transformation.  For  ex- 
ample, it  can  be  shown  that  a  pound  of 
good  coal,  if  thoroughly  burned  in  air,  is 
capable  of  yielding  a  total  amount  of 
energy  equal  to  15,500,000  joules,  or, 
11,440,000  foot-pounds.  Consequently,  if 
the  energy  so  liberated  were  applied  to 
drive  a  steam  engine,  this  steam  engine,  if 
burning  one  pound  of  coal  per  hour,  would 
be  able  to  raise  a  weight  .of  one  pound 
11,440,000  feet  in  that  time,  and  would, 
therefore,  be  exerting  an  activity  of  5.778 
horse-power,  or  4,310  watts.  In  point  of 
fact,  however,  the  best  steam  engines  and 
boilers  are  only  capable  of  delivering 


about  y^ths  of  one  horse-power-hour,  with 
one  pound  of  coal,  so  that  the  efficiency  of 


26  THE  ELECTRIC   MOTOR   AND 

such  an  engine  and  boiler  would  only  be 

0  8 
'       =  0.1385,  or  13.85  per  cent.,  and,  in 

o.77o 

fact,  with  the  types  of  engine  ordinarily 
employed,  the  efficiency  is  commonly  only 
about  8  per  cent. 

This  comparatively  low  efficiency  of  a 
steam  engine  and  boiler  is  due  to  the  com- 
bination of  two  very  different  causes. 
One  of  these  lies  in  the  working  tempera- 
ture, or  the  difference  in  temperature 
between  the  steam  admitted  to  the  engine 
and  the  steam  leaving  the  engine.  It  is  a 
law  of  nature  that  the  amount  of  heat 
which  can  be  mechanically  realized  from 
the  liberation,  during  combustion,  of  a 
given  quantity  of  chemical  energy, 
depends  upon  the  working  temperatures. 
With  the  working  temperatures  which  are 
imposed  by  practical  considerations  in  the 


THE  TRANSMISSION   OF   POWER.  27 

best  steam  engines,  the  efficiency  due  to 
this  cause  is  restricted  to  about  25  per 
cent.,  so  that  if  the  steam  engine  and 
boiler  were  perfect  machines,  losing  none 
of  the  power  which  was  capable  of  being 
delivered  to  them,  they  could  not  under 
these  circumstances  have  an  efficiency, 
taken  in  conjunction,  of  more  than  25 
per  cent.  The  balance  of  the  work  is 
uselessly  expended  in  heating  the  air  and 
water. 

The  second  source  of  loss  lies  in  the 
necessary  imperfections  of  engine  and 
boiler  as  machines.  The  above  losses  are 
due  to  frictions  and  loss  of  heat  by  con- 
duction, convection,  radiation  and  conden- 
sation. Retaining  the  same  working 
temperature,  these  losses  are  reduced  by 
all  improvements  in  the  engine  and  boiler, 
considered  as  machines  for  effecting  trans- 

o 


28  THE   ELECTRIC   MOTOR. 

formation  of  energy.  The  efficiency  of  an 
engine  and  boiler,  considered  as  receiving 
only  the  energy  which  is  rendered  available 
by  the  range  of  working  temperature,  is 
at  the  best  about  56  per  cent.,  so  that  the 
nett  efficiency,  reckoned  from  the  total 
chemical  energy  of  coal,  in  the  best  engines 
and  boilers  is  only  about  0.25  X  0.56=  0.14, 
or  14  per  cent. 


CHAPTER  III. 

ELEMENTARY    ELECTRICAL    PRINCIPLES. 

THE  grave  mistake  is  not  infrequently 
made  that  because  we  are  still  ignorant  of 
the  real  nature  of  electricity,  we  are  neces- 
sarily equally  ignorant  of  the  principles 
controlling  its  action.  In  point  of  fact 
the  engineer  has  to-day  a  more  intimate 
knowledge  of  the  laws  of  electricity,  than 
of  the  laws  which  govern  the  application 
of  steam.  Since,  in  the  study  of  the 
electric  motor,  a  knowledge  of  the  more 
important  laws  of  electricity  is  neces- 
sary, it  will  be  advisable  to  discuss  them 
briefly,  before  proceeding  further  with  the 
subject. 


30 


THE   ELECTRIC   MOTOR  AND 


All  electric  current,  or  electric  flow,  re- 
quires for  its  existence  a  complete  conduct- 
ing path  as  represented  in  Fig.  1.  Here 


6  VOLTS 
3  OHMS 

L 


3ROP1  VOLT 


2  AMPERES 


2  AMPERES 


2  AMPERES 


2  AMPERES 


DROPS  VOLTS 
2  AMPERES 
1  OHM 


s 


DROP1  VOLT 


E.M.F.  10  VOLTS 

FIG.  1. — ELECTRIC  CIRCUIT,   INCLUDING  SOURCE,  LAMP 
AND  CONDUCTING  LEADS. 

a  voltaic  battery,  or  other  electric  source, 
supplies  an  electric  current  through  the 
completed  circuit,  A  B  C  D.  Unless  a 
completed  path  be  provided  for  the  passage 


THE  TRANSMISSION   OF  POWER.  31 

of  the  electricity,  both  through  the  source 
and  the  external  circuit,  an  electric  current 
cannot  be  sustained.  All  practical  elec- 
tric circuits  of  this  character  consist  of 
three  separate  parts ;  namely, 

(1)  The  electric  source. 

(2)  Conducting  wires  or  leads. 

(3)  An     electro-receptive     device    tra- 
versed by  the  current. 

In  all  electric  circuits  of  this  type,  it  is 
convenient,  for  purposes  of  description,  to 
regard  the  electricity  as  leaving  the  source 
at  a  point  called  its  positive  pole,  and 
returning  to  the  source,  after  it  has  passed 
through  the  circuit  of  the  receptive  de- 
vices placed  therein,  to  a  point  called  its 
negative  pole.  The  current,  after  entering 
the  source,  flows  through  it  and  again 
emerges  at  its  positive  pole.  It  will  be 
seen  that  the  path  thus  traversed  by  the 


32  THE   ELECTRIC   MOTOR  AND 

current  is  circuital,  in  so  far  as  it  again 
reaches  the  point  from  which  it  started. 
The  conducting  path  forms  what  is  called 
an  electric  circuit.  It  must  not  be  sup- 
posed, however,  that  circuits  are  neces- 
sarily circular  in  outline,  since  a  circuit 
will  be  established  no  matter  what  the 
shape  of  the  conducting  path,  provided 
only  that  the  electric  flow  reaches  the 
point  from  which  it  is  assumed  to  have 
started. 

An  electric  circuit  is  said  to  be  made, 
completed,  or  closed,  when  a  complete  con- 
ducting path  is  provided  for  it.  It  is  said 
to  be  broken,  or  opened,  when  this  conduct- 
ing path  is  interrupted  at  any  point. 

When  an  electric  source,  such  as  shown 
in  Fig.  1,  is  open  or  broken,  the  current 
ceases  to  flow,  and,  consequently,  the 


THE  TRANSMISSION   OF   POWER.  33 

source  ceases  to  furnish  electricity.  It 
does  not,  however,  cease  to  furnish  a 
variety  of  force  called  electromotive  force. 
As  long  as  the  circuit  remains  open  the 
electromotive  force  produced  by  the  bat- 
tery does  no  work;  i.  e.,  expends  no 
energy.  It  is  only  when  a  conducting  cir- 
cuit is  provided  for  it,  that  it  can  produce 
a  motion  of  electricity  and  thus  do  work. 
In  point  of  fact  all  electric  sources  are 
to  be  regarded  as  sources  of  electromotive 
force,  usually  abbreviated  E.  M.  F.,  rather 
than  sources  of  current,  since  they  produce 
E.  M.  F.  whether  their  circuit  is  opened 
or  closed.  Morever,  the  conditions  of 
their  working  remaining  the  same,  the 
value  of  their  E.  M.  F.  remains  un- 
changed ;  whereas,  as  we  shall  see,  the 
value  of  the  current  they  produce,  de- 
pends entirely  upon  certain  conditions  of 
the  circuit  with  which  they  are  connected. 


"34  THE  ELECTRIC   MOTOR  AND 

Regarding  Fig.  1,  as  a  typical  instance 
of  a  working  electric  circuit,  provided,  as 
already  mentioned,  with  a  voltaic  battery, 
conducting  leads,  and  an  electro-receptive 
device  or  devices,  let  us  inquire  liow  we 
can  ascertain  the  amount  of  electricity  that 
will  flow  through  the  circuit  in  a  given 
time.  In  this,  as  in  any  similar  electric 
circuit,  the  strength  of  current  which  flows, 
that  is,  the  quantity  of  electricity  which 
passes  through  the  circuit  per  second,  is 
dependent  on  two  quantities ;  namely,  on 
the  value  of  the  E.  M.  F.,  which  may,  for 
convenience,  be  regarded  as  an  electric, 
pressure  causing,  or  tending  to  cause,  the 
electric  flow,  and  on  a  quantity  called  the 
resistance  of  the  circuit,  which  acts  so  as 
to  limit  the  quantity  of  electricity  passing 
through  the  circuit  in  a  given  time.  The 
current  strength  passing  is  related  to  these 
quantities  in  a  manner  discovered  by  Dr. 


THE  TRANSMISSION  OF  POWER.  35 

Ohm,  and  expressed  by  him  in  a  law, 
generally  known  as  Ohm's  law,  as  fol- 
lows: The  current  strength  in  any  circuit 
is  equal  to  the  E.  M.  F.,  acting  on  that 
circuit,  divided  by  the  resistance  of  the 
circuit. 

In  order  to  assign  definite  values  to  the 
above  quantities,  certain  units  are  em- 
ployed. The  units  in  international  use 
are  as  follows:  the  unit  of  E.  M.  F., 
called  the  volt;  the  unit  of  resistance, 
called  the  ohm,  and  the  unit  of  current 
strength  or  flow,  called  the  ampere.  Ohm's 
law,  expressed  in  terms  of  these  units, 
is  as  follows ;  namely, 

volts 

amperes  =  — , 

ohms 

Suppose,  for  example,  in  the  case  of  the 
simple  electric  circuit  shown  in  Fig.  1, 


36.  THE   ELECTRIC   MOTOR  AND 

that  the  E.  M.  F.  of  the  voltaic  battery  is 
10  volts,  and  the  resistance  of  the  entire 
circuit,  including  the  resistance  of  the 
source,  the  conducting  wires  and  the 
lamp,  is  5  ohms ;  then,  in  accordance 
with  Ohm's  law,  the  current  strength 

, ,  ,      10  volts 

would  be  — — ; =  2  amperes. 

D  ohms 

The  volt  is,  roughly,  equal  to  the 
E.  M.  F.  of  a  blue-stone  voltaic  cell,  such 
as  is  commonly  used  in  telegraphy.  The 
ohm  is  the  resistance  of  about  two  miles 
of  ordinary  trolley  wire,  and  the  ampere 
is  about  twice  as  strong  a  current  as  is 
ordinarily  used  in  a  16  candle-power,  110- 
volt,  incandescent  lamp. 

The  dynamo-electric  machine  is  the 
practical  source  of  the  powerful  electric 
currents  that  are  in  common  use. 


^*pw^f% 

fl^  PPr^r-^.  fy 

'  •vtjFiiRTv  &£ 

THE  TliANSl^I^ION  OF  POWER:    I        37 


.^  ^ 

/r-> 


Dynamos  can  be  extracted  to  give  an 
E.  M.  F.,  varying  fronT^fe^Mi^  t<> 
10,000  volts.  The  E.  M.  F.  employed  for 
street  railroad  systems  is  about  500  volts. 
The  E.  M.  F.  employed  for  continuous-cur- 
rent incandescent  electric  lighting  is  about 
115  volts. 

There  are  a  great  variety  of  voltaic 
cells.  The  value  of  the  E.  M.  F.  varies  in 
each,  but  in  general,  is  comprised  be- 
tween 2/3rds  volt  and  2  1/2  volts.  As 
this  pressure,  or,  as  it  is  frequently  called, 
voltage,  is  insufficient  to  operate  most 
receptive  devices,  it  is  necessary  to  in- 
crease it  by  connecting  a  number  of  sepa- 
rate cells  together  so  as  to  permit  them  to 
act  as  a  single  cell  or  battery.  Such  con- 
nection may  be  effected  in  various  ways, 
but  the  readiest  is  connection  in  series, 
which  consists  essentially  in  connecting  the 


38  THE   ELECTRIC    MOTOR   AND 

positive  pole  of  one  cell  to  the  negative 
of  the  next,  and  the  positive  of  this, 
to  the  negative  of  the  next,  and  so  on 
through  the  entire  number  of  cells,  as 


FIG.  2.— VOLTAIC  BATTERY  OF  THREE  CELLS  IN  SERIES. 

shown  in  Fig.  2,  where  three  separate, 
Daniell  gravity  cells  are  connected  in 
series.  If  the  E.  M.  F.  of  each  cell  is,  say 
1.1  volts,  the  E.  M.  F.  of  the  battery  will 
be  3.3  volts.  Dynamos  may  also  be  con- 
nected in  series,  but  since  it  is  easy  to 
construct  a  dynamo  for  the  full  E.  M.  F. 
required,  the  expedient  is  rarely  resorted  to. 


THE  TRANSMISSION  OF  POWER.  39 

The  resistance  offered  by  a  pipe  to  the 
flow  of  water  through  it  increases  with 
the  length  of  the  pipe  and  also  with  the 
narrowness  of  its  bore.  A  long,  narrow 
pipe  has  a  higher  resistance,  and  permits 
less  water  to  flow  through  it  in  a  given 
time,  and  under  a  given  pressure,  than  a 
short  pipe  of  large  diameter.  In  the  same 
way,  the  resistance  of  an  electric  wire 
increases  with  its  length  and  with  its 
narrowness.  A  long,  fine  wire  has  a  high 
resistance,  as  compared  with  a  short,  thick 
wire.  Thus,  one  foot  of  very  fine  copper 
wire,  No.  40  A.  W.  G.  (American  Wire 
Gauge),  having  a  diameter  of  0.003145 
inch,  has  a  resistance  of,  approximately, 
one  ohm.  If,  therefore,  the  length  of  a 
wire  be  fixed,  we  can  make  its  resistance 
almost  anything  we  please  by  altering  its 
area  of  cross-section.  If  we  double  the 
cross-section,  we  halve  the  resistance, 


40  THE   ELECTUIC   MOTOR   AND 

the  resistance  increasing  directly  with 
the  length,  and  inversely  with  the  cross- 
sectional  area  of  the  wire. 

There  is  another  way  of  varying  the  re- 
sistance of  wires  of  the  same  dimensions ; 
i.  e.j  by  employing  different  materials.  In 
other  words,  the  resistance  of  a  wire 
depends  not  only  upon  its  length  and 
cross-section,  but  also  upon  the  nature  of 
its  su  bstance.  The  specific  resistance  of  iron 
is  about  61/2  times  as  great  as  that  of 
copper,  so  that  a  wire  of  iron  would  have 
6  1/2  times  as  much  resistance  as  a  wire 
of  copper  having  the  same  length  and 
cross-section. 

In  order  to  compare  readily  the  specific 
resistances  of  different  materials,  reference 
is  had  to  a  quantity  called  the  resistivity. 
The  resistivity  of  a  material  is  the  resist- 


THE   TRANSMISSION   OF   POWER.  41 

ance  offered  by  a  wire  having  unit  length 
and  unit  cross-sectional  area.  These  unit 
values  are  generally  taken  as  one  centi- 
metre for  the  length,  and  one  square  centi- 
metre for  the  area  of  cross-section,  so  that, 
when  we  speak  of  the  resistivity  of  copper 
as  being  1.6  microhms,  we  mean  that  a 
wire  1  centimetre  in  length  and  having  a 
cross-section  of  1  square  centimetre,  has  a 
resistance  of  1.6  microhms;  i.  e.,  1.6  mil- 

Months  of  an  ohm     -J.     The  resist- 


ance  of  one  metre  of  this  wire  would  be 

1.6  x  100 

—  —         =160  microhms,  and  the  resist- 

ance of  one  metre  of  a  wire  having  a  cross- 
sectional    area    of    2   square    centimetres 

in  ,     1.6  x  100 
would  be  -  -  =  80  microhms.     Con- 

2i 

sequeritly,  if  the  resistivity  of  a  material  is 
known,  it  is  easy  to  determine  what  the 


42  THE   ELECTRIC   MOTOR  AND 

resistance  of  any  uniform  wire  will  be  of 
given  length  and  cross-sectional  area. 

In  English-speaking  countries,  where 
lengths  are  generally  measured  in  feet,  and 
the  diameters  of  wires  in  inches,  it  is  con- 
venient to  employ  as  an  area  of  cross-sec- 
tion the  circular  mil.  A  mil  is  a  unit  of 
length  of  the  value  of  one  thousandth  of 
an  inch,  and  a  wire,  one  inch  in  diame- 
ter, is  said  to  have  a  diameter  of  1,000 
mils.  If  we  square  the  diameter  of  a  wire 
in  mils,  we  obtain  its  area  in  circular  mils, 
so  that  a  circular  wire,  one  inch  in  diame- 
ter, has  an  area  of  one  million  circular  mils, 
A  circular  mil-foot  is  a  unit  of  cross-sec- 
tion and  length  possessed  by  a  wire  one 
foot  long  and  having  a  diameter  of  one 
mil,  and,  consequently,  an  area  of  one  cir- 
cular mil.  A  circular  mil-foot  of  copper 
has  a  resistance  of  10.35  ohms,  at  20°  C. ; 


THE  TRANSMISSION    OK    l»o\VI-:iI.  43 

so  that  if  a  wire  be  one  mile  long,  and 
have  a  diameter  of  0.2  i noli,  its, :  cross-sec* 
tion  will  be  200  X  200  =  40,000  circular 
mils,  and  its  length  will  be  5,280  feet,  so 

5,280  X  10.35 
that  its  resistance  will  be  - 

1.366  ohms  at  20°  C. 

The  resistivity  of  all  metals  is  increased 
by  an  increase  in  temperature.  In  most 
metals  this  increase  is  about  0.4  per  cent, 
per  degree  Centigrade,  reckoned  from  the 
resistivity  at  zero  Centigrade,  so  that,  at 
the  temperature  of  boiling  water,  the 
resistivity  of  copper  is  about  40  per  cent, 
greater  than  its  resistivity  at  the  freezing 
point  of  water.  In  computing  the  resist- 
ance of  a  wire,  therefore,  its  temperature 
must  be  taken  into  account. 

AVhen  a  current  of  water  flows  through 
a  pipe,  the  quantity  of  water  which  passes 


44  THE   ELECTRIC   MOTOR  AND 

depends  both  on  the  flow,  and  on  the  time 
during  which  the  flow  takes  place.  In 
the  same  way  the  quantity  of  electricity 
which  passes  through  a  wire  depends  both 
on  the  rate  of  flow,  or  the  number  of 
amperes,  and  on  the  time  during  which 
the  flow  takes  place.  In  determining  the 
quantity  of  water  which  passes  through  a 
pipe,  the  gallon  is  frequently  employed 
as  a  unit  of  quantity.  Similarly,  in 
determining  the  quantity  of  electricity 
which  passes  through  a  wire,  a  unit  of 
electric  quantity  called  the  coulomb  is 
employed.  As  in  water  currents,  the 
gallon-per-second  might  be  employed  as 
the  unit  of  current,  so  in  the  electric  cur- 
rent, the  unit-rate-of-flow  is  taken  as  a 
coulomb-per-second,  a  rate  of  flow  the  same 
as  the  ampere  already  referred  to.  The 
coulomb  is,  therefore,  the  quantity  of 
electricity  which  passes  through  a  circuit 


THE  TRANSMISSION  OF  POWER.        45 

during  one  second,  when  the  current 
strength  is  one  ampere.  Thus,  again 
referring  to  the  simple  electric  circuit 
shown  in  Fig.  1,  the  value  of  the  current 
flowing  through  which  was  calculated 
as  two  amperes,  the  quantity  of  electricity 
would  be  two  coulombs  in  each  second,  or 
120  coulombs  per  minute. 

A  reservoir  filled  with  water  may  be 
regarded  as  a  store  of  energy  and  can  be 
caused  to  expend  that  energy  in  doing 
work,  by  permitting  the  water  to  escape 
so  as  to  drive  a  water  motor.  The 
amount  of  energy,  which  can  be  trans- 
ferred from  the  reservoir  to  the  motor, 
will  depend  both  on  the  quantity  of  water 
in  the  reservoir,  and  on  the  vertical  height 
through  which  the  water  is  permitted  to 
fall.  Thus,  if  the  reservoir  contain  1,000,- 
000  pounds  of  water,  and  this  drives  a 


48  ME  ELECTKIC   MOTOR   AND 

E.  M.  F.  of  10  volts  is  active.  This  pres- 
sure corresponds  to  the  total  difference  of 
level  between  the  water  in  the  reservoir 
and  the  motor  which  it  drives.  Every 
coulomb  of  electricity  which  flows  through 
this  circuit  requires  an  expenditure  of 
work  equal  to  10  volts  X  1  coulomb  =  10 
volt-coulombs  =  10  joules  =  7.38  foot- 
pounds. Since,  as  we  have  seen,  the 
current  strength  iu  this  circuit  is  2 
amperes ;  i.  e.,  2  coulombs-per-second,  the 
work  done  will  be  2  X  10  =  20  joules 
in  each  second.  A  joule-per-second  is 
called  a  watt ;  consequently,  the  activity 
in  this  circuit  will  be  20  watts.  In  any 
electric  circuit  the  rate  at  which  work  is 
being  expended  ;  i.  e.,  the  activity  of  the 
circuit,  expressed  in  watts,  is  equal  to  the 
product  of  the  total  pressure  in  volts 
multiplied  by  the  current  strength  in 
amperes. 


THE   TRANSMISSION   OF   POWER.  49 

This  activity  has  to  be  supplied  to  the 
circuit  by  the  electric  source.  In  the  case 
of  a  dynamo,  the  activity  is  supplied  by 
the  engine  or  turbine  driving  the  dynamo. 
In  the  case  of  a  battery,  the  activity  is 
supplied  by  the  chemical  energy  of  the 
cell,  in  other  words,  by  the  burning  of  the 
zinc  in  the  battery  solution. 

The  activity  so  expended  in  an  electric 
circuit  appears  in  one  of  three  ways : 

(1)  Heat. 

(2)  Mechanical  work. 

(3)  Electro-chemical  work. 

The  relative  expenditure  of  activity  in 
these  three  different  ways  is  determined 
by  the  distribution  of  what  is  called  the 
counter  E.  M.  F.y  abbreviated  C.  E.  M.  F. 
For  example,  in  Fig.  1,  an  E.  M.  F.  of  10 
volts  acting  in  the  circuit  is  opposed  by 


48  THE   ELECTRIC   MOTOK   ANT) 

E.  M.  F.  of  10  volts  is  active.  This  pres- 
sure corresponds  to  the  total  difference  of 
level  between  the  water  in  the  reservoir 
and  the  motor  which  it  drives.  Every 
coulomb  of  electricity  which  flows  through 
this  circuit  requires  an  expenditure  of 
work  equal  to  10  volts  X  1  coulomb  =  10 
volt-coulombs  =  10  joules  =  7.38  foot- 
pounds. Since,  as  we  have  seen,  the 
current  strength  in  this  circuit  is  2 
amperes ;  i.  e.,  2  coulombs-per-second,  the 
work  clone  will  be  2  x  10  =  20  joules 
in  each  second.  A  joule-per-second  is 
called  a  watt;  consequently,  the  activity 
in  this  circuit  will  be  20  watts.  In  any 
electric  circuit  the  rate  at  which  work  is 
being  expended  ;  i.  e.,  the  activity  of  the 
circuit,  expressed  in  watts,  is  equal  to  the 
product  of  the  total  pressure  in  volts 
multiplied  by  the  current  strength  in 
amperes. 


>THE   TRANSMISSION   OF   POWER.  49 

This  activity  has  to  be  supplied  to  the 
circuit  by  the  electric  source.  lu  the  case 
of  a  dynamo,  the  activity  is  supplied  by 
the  engine  or  turbine  driving  the  dynamo. 
In  the  case  of  a  battery,  the  activity  is 
supplied  by  the  chemical  energy  of  the 
cell,  in  other  words,  by  the  burning  of  the 
zinc  in  the  battery  solution. 

The  activity  so  expended  in  an  electric 
circuit  appears  in  one  of  three  ways : 

(1)  Heat. 

(2)  Mechanical  work. 

(3)  Electro-chemical  work. 

The  relative  expenditure  of  activity  in 
these  three  different  ways  is  determined 
by  the  distribution  of  what  is  called  the 
counter  E.  M.  F.,  abbreviated  C.  E.  M.  F. 
For  example,  in  Fig.  1,  an  E.  M.  F.  of  10 
volts  acting  in  the  circuit  is  opposed  by 


50  THE  ELECTRIC   MOTOR   AND 

a  C.  E.  M.  F. ;  i.  e.,  a  back  pressure,  or 
oppositely  directed  E.  M.  F.  opposing  the 
flow  of  the  current. 

The  passage  of  water  through  a  pipe  is 
always  attended  by  a  back  pressure.  For 
example,  if  a  powerful  stream  of  water  be 
forced  through  a  long  hose,  there  will  be 
a  difference  of  pressure  between  the  two 
ends  of  the  hose,  owing  to  the  resistance 
encountered  by  the  water  during  the  pas- 
sage. If  the  water  escapes  freely  from  the 
distant  end  into  the  air,  the  pressure  in  the 
hose,  at  a  distance  of  say  two  hundred  feet 
from  the  end,  may  be,  perhaps,  five  pounds 
per  square  inch  above  the  pressure  of  the 
air.  This  is  the  back  pressure  due  to 
the  flow  of  water.  It  increases  with  the 
rapidity  of  the  discharge. 

In  an  electric  conductor  or  circuit,  the 


THE  TRANSMISSION   OF  POWER.  51 

product  of  the  current  strength  in  amperes 
and  the  resistance  in  ohms,  gives  the  back 
pressure,  or  C.  E.  M.  F.  in  volts.  Thus  in 
the  circuit  of  Fig.  1,  where  the  resistance 
of  the  entire  circuit  is  5  ohms,  and  the 
current  2  amperes,  the  C.  E.  M.  F.  is 
2x5=  10  volts,  which  is  equal  to  the 
driving  E.  M.  F .  This,  in  fact,  follows 
from  a  consideration  of  Ohm's  law; 
namely,  that  the  E.  M.  F.  divided  by  the 
resistance  gives  the  current  strength,  so 
that  the  current  strength  multiplied  by 
the  resistance,  is  equal  to  the  E.  M.  F. 

Since  the  resistance  of  the  circuit,  shown 
in  Fig.  1,  is  made  up  of  the  resistance  of 
the  voltaic  battery,  the  conducting  wires 
and  the  lamp,  the  C.  E.  M.  F.  or  fall  of 
pressure  of  10  volts,  is  distributed  in  these 
portions  according  to  their  respective  re- 
sistances. If  the  resistance  of  the  battery 


52  THE   ELECTRIC   MOTOR  AND 

be  1  ohm,  that  is,  if  the  battery  con- 
sidered as  an  electric  conductor  composed 
of  liquids  and  metals,  offered  a  resistance 
of  1  ohm  to  the  passage  of  the  current 
it  generates,  the  C.  E.  M.  F.  set  up  in  the 
battery  by  the  current  strength  of  2 
amperes  will  be  2  amperes  X  1  ohm  = 
2  volts.  Or,  regarded  from  the  standpoint 
of  Ohm's  law,  2  volts  will  be  the  E.  M. 
F.  necessary  to  force  2  amperes  through 
the  resistance  of  the  battery.  As  it  is 
usually  expressed,  the  " drop"  or  fall  of 
pressure  in  the  resistance  of  the  battery 
will  be  2  volts.  Again,  if  the  resistance 
of  the  conducting  wires  leading  to  the 
lamp ;  i.  e.,  the  leads,  be  1  ohm,  or  1/2 
an  ohm  in  each  conductor,  the  drop  in  each 
will  be  2  amperes  X  1/2  ohm  =  1  volt. 
Since  the  resistance  of  the  lamp  is  3 
ohms,  the  C.  E.  M.  F.,  or  drop  in  its  resis- 
tance, will  also  be  2  amperes  x  3  ohms  = 


THE  TRANSMISSION   OF   POWER.  53 

6  volts.  The  total  drop,  or  C.  E.  M.  F. 
due  to  resistance,  will,  therefore,  be  6  volts 
in  the  lamp,  2  volts  in  the  conducting 
wires,  and  2  volts  in  the  battery,  making 
the  total  C.  E.  M.  F.  equal  and  opposite 
to  the  driving  E.  M.  F. ;  namely  10  volts. 

As  we  have  seen,  the  activity  expended 
by  a  source  is  the  product  of  the  driving 
pressure  or  E.  M.  F.  in  that  source,  and  the 
current  strength  in  the  circuit  expressed 
in  coulombs-per-secoud,  or  amperes.  Simi- 
larly, the  activity  in  watts,  expended  on 
a  source  of  C.  E.  M.  F.,  is  the  product  of 
that  C.  E.  M.  F.  in  volts,  and  the  cur- 
rent strength  passing  through  the  circuit. 
Thus,  the  activity  expended  in  the  lamp 
of  Fig.  1,  will  be  6  volts  x  2  amperes  = 
12  watts,  or  8.856  foot-pounds-per-second, 
expended  in  the  lamp  as  heat.  Again,  the 
activity  expended  in  the  two  conductors  is 


54  THE   ELECTRIC   MOTOR   AND 

2  volts  x  2  amperes  =  4  watts,  or  2.952 
foot-poimds-per-second.  The  activity  ex- 
pended in  the  internal  resistance  of  the 
battery  will  be  also  2  volts  x  2  amperes  = 
4  watts  —  2.952  foot-pounds-per-second, 
while  the  activity  expended  in  the  entire 
circuit  of  the  battery  will  be  10  volts  x 
2  amperes  =  20  watts  =  15.76  foot-pounds- 
per-second. 

Summing  up  the  various  activities  in 
the  circuit,  we  have,  as  follows;  viz., 

The  activity  expended  on  the  circuit  by 
the  source  is  10  volts  X  2  amperes  =  20 
watts  =  20  joules-per-second.  Of  this  the 
activity  expended  in  the  circuit  by  the 
lamp  is  6  volts  X  2  amperes  =12  watts; 
the  activity  expended  in  the  two  leads,  is  2 
volts  x  2  amperes  =  4  watts;  the  activity 
expended  in  the  battery,  is  2  volts  X  2  am- 
peres =  4  watts ;  total  activity  =  20  watts. 


THE 


DIESEL  fl 

OF   POWER. 


In   the 

pended  by  the  c^ji^cal  energy  in  the  bat- 
tery, and  is  liberale^efitii'ely  in  the  form 
of  heat  ;  that  is  to  say,  the  battery  is 
warmed,  the  wires  are  warmed,  and  the 
lamp  is  warmed.  The  lamp  becomes 
much  hotter  than  either  the  battery  or 
the  wires,  because  the  heat  is  liberated  in 
a  very  small  volume  of  material,  and  can 
escape  only  from  a  very  contracted  sur- 
face. All  activity  expended  against  the 
C.  E.  M.  F.  of  drop  is  thermal  activity  and 
is  usually  to  be  considered  as  wasted 
activity,  except  in  the  case  of  electric 
heaters  or  electric  lamps,  where  this 
C.  E.  M.  F.  and  activity  are  designedly 
employed  for  warming  the  surrounding  air 
or  other  bodies. 

When  an  electric  motor  is  so  placed  in 
any  circuit,  that  a  current  passes  through  it, 


56 


THE   ELECTRIC    MOTOR   AND 


there  will  be  produced  in  it  a  drop  or  C. 
E.  M.  F.  due  to  resistance  only  ;  provided 
that  the  motor  be  prevented  from  moving. 
If,  however,  the  motor  be  driven  by  the 


FIG.  3. — ELECTRIC  CIRCUIT  CONTAINING  SOURCE,  LEADS 
AND  MOTOR. 

current,  then  there  is  produced  an  addi- 
tional C.  E.  M.  F.  which  is  generated  by 
the  rotation  of  the  motor.  Thus,  if  the 
motor  M,  in  Fig.  3,  has  a  resistance  of  1 


THE   TRANSMISSION   OF   POWER.  57 

ohm,-  and  the  leads  to  the  motor  have  each 
a  resistance  of  1  ohm,  while  the  internal 
resistance  of  the  battery  or  electric  source 
is  also  1  ohm,  then  the  total  resistance 
of  the  circuit  will  be  4  ohms,  and,  as  long 
as  the  motor  is  prevented  from  running, 
the  current  strength  in  the  circuit  will  be 
10  volts  divided  by  4  ohms  =  2.5  amperes. 
The  activity  expended  by  the  source  will, 
therefore,  be  10  volts  x  2.5  amperes  =  25 
watts,  and  this  activity  will  be  entirely 
expended  in  heating  the  circuit.  6  1/4 
watts  will  be  expended  in  warming  the 
battery,  6  1/4  watts  in  warming  each 
wire,  and  61/4  watts  in  warming  the  wire 
wound  upon  the  motor. 

If,  however,  the  motor  be  permitted  to 
run,  and,  therefore,  to  do  work,  it  must 
expend  energy ;  and  this  expenditure  must 
be  supplied  from  the  circuit  as  the  pro- 


58  THE   ELECTRIC   MOTOR  AND 

duct  of  a  C.  E.  M.  F.  and  the  current 
strength  which  it  opposes.  Thus,  if  the 
motor  by  its  rotation  generates  a  C.  E. 
M.  F.  of  2  volts,  in  addition  to  its 
C.  E.  M.  F.  of  drop,  the  E.  M.  F.  acting 
on  the  circuit  will  be  10  volts  in  the  bat- 
tery, less  2  volts  C.  E.  M.  F.  of  rotation 
produced  by  the  motor,  or  8  volts,  as  the 
resultant  driving  E.  M.  F.,  capable  of  be- 
ing expended  in  forcing  current  through 
the  circuit  against  resistance.  The  current 
strength  will,  therefore,  be  8  volts  -r-  4 
ohms  =  2  amperes,  and  the  activity  of  the 
source  will  be  10  volts  x  2  amperes  =  20 
watts  =  14.76  foot-pounds.  The  drop  in 
the  battery  will  be  2  amperes  X  1  ohm  = 
2  volts ;  that  in  each  of  the  leads  2  volts  ; 
and  that  in  the  winding  of  the  motor  2 
volts.  The  total  pressure  at  motor  termi- 
nals is,  therefore,  4  volts.  The  activity 
expended  as  heat  will,  therefore,  be  2  volts 


THE  TRANSMISSION   OF   POWER.  59 

X  2  amperes  =  4  watts  in  the  battery,  4  in 
each  of  the  wires,  and  4  in  the  motor 
winding  =  16  watts  in  all.  The  activity 
in  the  motor  available  for  mechanical 
work,  is,  however,  the  C.  E.  M.  F.  of  rota- 
tion, or  2  volts  x  2  amperes  =  4  watts,  so 
that  the  total  amount  of  work  which  the 
motor  can  perform  mechanically  is  4  watts, 
or  2.952  foot-pounds-per-second.  It  is  to 
be  observed,  therefore,  that  while  20  watts 
are  expended  by  the  source,  only  4 
watts  can  in  this  instance  be  utilized  for 
mechanical  purposes,  the  balance  being 
expended  in  heating  the  circuit. 

Analyzing  the  activity  in  the  circuit  we 
have :  Total  activity  of  battery  10  volts 
x  2  amperes  =  20  watts  =  14.76  foot- 
pounds-per-second.  This  must  be  ex- 
pended in  the  circuit  as  a  whole.  The 
drop,  or  C.  E.  M.  F.  due  to  resistance  in 


60  THE   ELECTRIC   MOTOR   AND 

the  two  leads,  is  4  volts,  so  that  the 
activity  in  wanning  the  leads  is  4  volts  x 
2  amperes  —  8  watts.  The  drop  in  the 
battery  is  2  volts,  so  that  the  activity  in 
warming  the  battery  is  2  volts  x  2  amperes 
—  4  watts.  The  drop  in  the  motor  is  2 
volts;  the  C.  E.  M.  F.  of  rotation  is  2 
volts;  the  total  C.  E.  M.  F.  is  4  volts. 
The  activity  in  the  motor  is,  therefore,  4 
volts  X  2  amperes  =  8  watts ;  total,  20 
watts.  Of  the  8  watts  total  activity  in 
motor,  4  watts  will  be  expended  in  heating 
its  wire,  and  4  watts  in  producing  rota- 
tion. 

We  have  already  referred  to  the  fact 
that  when  water  escapes  from  a  reservoir 
through  a  pipe  a  back  pressure,  or  a  coun- 
ter watermotive  force  is  produced  in  the 
pipe,  tending  to  check  the  flow.  Fig.  4, 
represents  a  reservoir  7?,  maintained  at  a 


THE   TRANSMISSION   OF   POWER. 


61 


practically  constant  level.  Suppose  a 
horizontal  pipe  B  O,  be  provided  with 
an  outlet  at  O.  If  the  outlet  at  O,  be 
temporarily  closed,  then  the  pressure  from 
the  water  in  j5,  will  cause  the  water  to 

01        23456       789      10 


t 

^    . 

rt* 

^ 

f* 

•  ~~~ 

*-- 

g 

f 

R 

""  -~ 

jj 

—  .  . 

L 

£ 

1 

1 

3     C 

»      1 

)      i 

:     £ 

1     <j 

Ir       k 

L      I 

i 

C     1 

j     G 

FIG.  4. — RESERVOIR  DISCHARGING  WATER  THROUGH  AN 
OUTLET  PIPE. 


stand  at  the  same  level  A  A',  in  all  the 
vertical  pipes,  1,  2,  3,  4,  etc.  If,  however, 
the  outlet  pipe  be  opened,  the  pressure 
at  the  outlet  will  fall  to  zero  ;  i.  e.,  become 
that  of  the  pressure  in  the  air,  and  the 
liquid  will  escape  owing  to  the  difference 
of  pressure  between  this  point  and  that 


62  THE   ELECTRIC    MOTOIl   AND 

in  the  reservoir.  There  will,  therefore, 
be  established  a  gradient  of  pressure  b  C\ 
which  will  be  practically  uniform  if  the 
pipe  be  uniform,  and  the  pressure  in  the 
pipe  will  be  represented  by  tbe  respective 
columns  of  water  at  Z>,  <?,  d,  e,  /,  etc.  The 
back  pressure  at  the  reservoir,  due  to  the 
flow  of  water  through  the  pipe,  is  l>  B,  or 
the  fall  of  pressure  in  the  reservoir.  At 
1,  the  back  pressure  is  represented  by 
the  column  c  C,  and  the  drop  of  pressure 
in  the  length  B  C,  is  represented  by  the 
column  of  water  c  c.  Similarly,  the  back 
pressure  at  2,  is  represented  by  the 
column  d  I),  and  the  drop  in  the  length 
CD,  bjr  the  column  dd'.  Similarly,  the 
drop  in  the  whole  length  B  O,  is  b  B, 
or  A'  O.  In  other  words,  the  pressure 
b  B,  is  that  which  is  required  to  produce, 
through  the  resistance  of  the  pipe,  the 
actual  flow  which  takes  place  through  it. 


THE  TRANSMISSION    OF   POWER.  63 

If  we  consider  a  pound  of  water  in  the 
pipe  after  leaving  the  reservoir,  then  when 
this  pound  of  water  has  reached  the 
point  1,  it  has  virtually  fallen  through  the 
height  c  c',  and,  therefore,  the  amount  of 
work  expended  by  the  reservoir  in  forc- 
ing the  water  through  the  pipe  against 
this  back  pressure  c  c',  will  be  this  pound 
multiplied  by  the  number  of  feet  in 
c  c'.  Again,  if  the  flow  from  the  reservoir 
be  say  50  pounds-per-second,  then  the  ex- 
penditure of  activity  in  foot-pounds-per- 
second,  will  be  50  pounds  x  height  O  A'. 
If  this  be  10  feet,  the  activity  of  the  reser- 
voir will  be  50  X  10  =  500  foot- pounds-per- 
second  =  678  watts. 

The  preceding  principles  are  those, 
which  as  we  have  seen,  apply  to  the  elec- 
tric circuit.  If  we  represent  the  number 
of  pounds  of  water  by  the  coulombs,  the 


64  THE   ELECTRIC   MOTOR   AND 

difference  of  level  in  feet,  by  the  volts, 
and  the  pounds-per-second,  by  the  amperes, 
the  analogy  is  complete :  for,  if  we  multiply 
the  current  flow  in  amperes,  by  the  drop 
of  pressure  caused  by  the  resistance  in 
volts,  we  have  the  joules-per-second,  or  the 
watts  of  activity,  expended  by  the  electric 
source  in  order  to  drive  the  electricity 
through  the  circuit  against  its  resistance, 
or  against  the  C.  E.  M.  F.  which  this  resist- 
ance produces.  It  must  be  remembered, 
however,  that  electricity  is  not  a  gross 
liquid  like  water  and  that  these  are  merely 
analogies. 


Fig.  5  represents  a  reservoir  with  an  out- 
let pipe  as  before,  but  coupled  to  a  small 
water  motor  M,  inserted  in  the  pipe.  This 
water  motor  absorbs  activity  by  reason  of 
the  back  pressure  it  is  capable  of  develop- 
ing when  in  rotation.  It  will  be  observed 


THE  TRANSMISSION    OF   POWER. 


65 


that  the  driving  pressure  in  the  reservoir  is 
now  equal  to  the  sum  of  the  drops  of  pres- 
sure in  the  pipe,  and  the  back  pressure  of 
the  motor  M.  Thus  dly  is  the  drop  of  pres- 
sure in  the  first  section  of  the  pipe,  d^  the 


B 


FIG.  5. — DISTRIBUTION  OF  PRESSURES   IN   MOTOR   AND 
PIPE. 

drop  of  pressure  in  the  second  section  of 
the  pipe,  and  I>,  is  the  back  pressure  due 
to  the  action  of  the  motor,  so  that  dly  B, 
and  dfy  are  together  equal  to  P. 

The  activity  expended  by  the  reservoir  in 
forcing  the  water  through  the  pipe  and 
motor  together,  is  equal  to  the  flow,  say 
50  pound s-per-second,  multiplied  by  the 


66  THE    ELECTRIC    MOTOR   AND 

total  driving  head  JP,  say  10  feet  =  50  x 
10  =  500  foot-pounds-per-second.  Of  this 
activity  that  which  is  expended  in  forcing 
the  water  through  the  pipe,  against  the  drop 
of  pressure  due  to  its  resistance,  is  ex- 
pended in  warming  both  the  pipe  and  the 
water,  while  the  activity  expended  against 
the  back  pressure  J3J  of  the  motor,  may  be 
entirely  employed  in  producing  mechanical 
work,  and  would  be  so  expended  if  the 
motor  J/,  were  a  perfect  machine.  Thus 
if  c/l7  be  2  feet  and  d%,  2  feet,  while  B,  is 
6  feet,  the  activity  expended  in  heating 
the  pipe  and  its  contents  is  4  feet  X  50 
pounds-per-second  =  200  foot-pounds-per- 
second  ;  while  the  activity  expended  in  the 
motor  is  6  feet  x  50  pounds-per-second  = 
300  foot-pounds-per-second.  Moreover,  the 
larger  the  pipe,  and  the  shorter  its  length, 
the  less  will  be  the  drop  for  a  given  flow, 
and  the  greater  the  proportion  of  activity 


THE   TRANSMISSION    OF   POWER.  67 

which    may  be  expended    in    driving  the 
motor. 

The  electric  analogue  is  shown  in  Fig. 
6,  where   the   source   is   represented  as  a 


;d> 


[±3 

FIG.  6. — ELECTRIC    ANALOGUE    SHOWING    DISTRIBUTION 
OF  PRESSURE  IN  MOTOR  AND  WIRES. 


battery  or  dynamo  producing  the  E.  M.  F. 
or  difference  of  electric  level  E.  The  cir- 
cuit A.  I),  extends  from  one  pole  of  the 
battery  to  the  other,  although  not  so  shown 
in  the  drawing.  The  motor  M,  produces  a 
back  pressure  B,  which  we  may  assume  to 
be  entirely  due  to  its  rotation,  the  resist- 
ance of  the  motor  being  negligible  ;  the  re- 


68  THE   ELECTRIC   MOTOR   AND 

sistance  of  the  conducting  wires  is  2  ohms 
each,  the  drop  in  the  conducting  wires  is 
represented  by  d^  and  d%,  as  before,  but 
expressed  in  volts  instead  of  in  feet.  If 
the  E.  M.  F.  at  generator  terminals  be  10 
volts,  d±  and  d2,  each  2  volts,  and  the  back 
pressure  of  the  motor  6  volts,  then  the 
current  through  the  circuit  will  be  10  - 
6  =  4  volts  divided  by  4  ohms  =  1  ampere. 
The  activity  expended  by  the  source  will  be 
10  volts  x  1  ampere  =10  watts  =  7.38  foot- 
pounds-per-second.  The  activity  expended 
in  each  of  the  leads  will  be  2  volts  X  1 
ampere  =  2  watts,  or  4  watts  in  all,  and 
the  balance,  or  6  watts,  must  be  equal  to 
the  activity  expended  in  the  motor ;  namely, 
6  volts  x  1  ampere.  If  the  motor  could  be 
made  perfect,  it  would  supply  6  watts 
mechanically  at  its  shaft,  or  4.428  foot- 
pounds-per-second,  available  for  driving 
purposes,  and  the  proportion  of  the  avail- 


THE   TRANSMISSION    OF   POWER.  t>9 

able  activity  in  the  circuit  to  the  total  activ- 

r* 

ity  expended  would  be  —  =  60  per  cent. 

In  practice,  owing  to  the  existence  of  vari- 
ous f rictional  forces  in  the  motor,  its  output 
would  be  less  than  6  watts,  say  4,  making 


E( 


m 

FIG.  7. — DISTKIBUTION   OP    ELECTRIC    PKESSUKE   IN   A 
CIRCUIT. 


its  efficiency  —  =  66  2/3  per  cent.,  and  the 

4 
efficiency  of  the  circuit  —  =  40  per  cent. 


Fig.  7  represents  a  more  nearly  com- 
plete analysis  of  the  distribution  of  drop 
and  expenditure  of  energy  in  a  circuit 


70  THE  ELECTRIC   MOTOR   AND 

consisting  of  a  source,  a  motor  and  conduct- 
ing wires. 

The  E.  M.  F.  of  the  battery  or  source 
is  represented  by  JK.  The  resistance  of 
the  battery  by  the  length  O  A,  the  resist- 
ance of  conducting  wires  by  the  lengths 
A  B  and  CD,  arid  the  resistance  of  the 
motor  by  the  length  B  C.  Then,  if  e  /, 
represents  the  back  pressure  of  the  motor 
due  to  its  rotation,  the  pressure  in  the  cir- 
cuit will  follow  the  line  o  a  b  f  e  c  D.  If 
0  o,  represents  10  volts,  0  A,  1  ohm,  A  B 
and  C  D  2  ohms  each,  B  C,  I  ohm,  then 
the  total  resistance  of  the  circuit  will  be 
6  ohms.  Also,  if  the  back  pressure  e  /, 
be  4  volts,  the  total  E.  M.  F.  in  the  circuit 
available  for  producing  current  through 
resistance  will  be  10  —  4  =  6  volts,  so  that 
by  Ohm's  law  the  current  strength  will  be 
6  volts  divided  by  6  ohms  =  1  ampere. 


THE   TRANSMISSION    OF   POWER.  71 

The  activity  expended  in  the  source  will 
be  1  watt;  that  in  the  conducting  wires 
4  watts ;  and  that  in  the  resistance  of  the 
motor  1  watt,  making  a  total  thermal  ac- 
tivity of  6  watts,  and  leaving  an  activity 
of  4  watts  to  be  expended  in  the  motor 
available  for  purpose  of  producing  rota- 
tion. As  a  matter  of  fact,  however,  the 
back  pressure  in  the  motor  is  not  devel- 
oped at  any  one  spot,  say  halfway 
through  its  resistance,  but  will  probably 
be  developed  uniformly  through  all  parts 
of  the  resistance,  and  the  combined  effect 
of  C.  E.  M.  F.  due  to  rotation  and  drop  in 
resistance  will  be  indicated  by  the  dotted 
line  b  c,  having  a  different  gradient  to  the 
line  o  b,  or  c  D. 

It  will  be  observed  that  the  drop  in  the 
battery  is  the  difference  in  pressure  be- 
tween E,  and  A  a,  or  0  o.  The  drop  in 


72  THE   ELECTRIC   MOTOR. 

the  leads  will  be  the  difference  in  pressure 
between  A  a  and  JB  £,  and  between  Co 
and  i>,  respectively.  The  total  drop  in 
the  motor  will  be  b  g,  or  the  difference 
between  B  b  and  C  c.  This  drop  is  com- 
posed of  two  parts ;  namely,  e  f,  due  to 
rotation  which  would  disappear  when  the 
motor  came  to  rest,  and  which  represents 
the  C.  E.  M.  F.  available  for  useful  work, 
and  the  difference  between  e  f  and  b  g, 
which  is  the  drop  in  the  resistance  of  the 
motor  with  a  current  of  one  ampere. 


CHAPTER  IV. 

EARLY    HISTORY     OF    THE    ELECTROMAGNETIC 
MOTOE. 

PROBABLY  one  of  the  most  valuable  gifts 
of  electromagnetic  science  to  the  industrial 
world  is  that  of  the  electromagnetic 
motor.  The  history  of  this  subject  is  not 
only  interesting  on  its  own  account,  but 
also  affords,  perhaps,  the  best  line  that  can 
be  followed  in  the  discussion  of  its  theory. 

The  electric  motor,  as  it  exists  to-day,  is 
a  marvel  of  ingenuity.  As  a  means  for 
converting  electrical  into  mechanical  en- 
ergy it  cannot  but  be  regarded  as  an  ex- 
ceptionally efficient  piece  of  apparatus. 

73' 


74  THE   ELECTRIC    MOTOR    AND 

Like  other  great  achievements,  the  electric 
motor  has  not  been  the  product  of  any 
single  man  or  nation,  but  is  rather  the 
embodiment  of  the  life  work  of  many  able 
workers,  from  many  countries,  through 
many  years.  As  Emerson  has  aptly  ex- 
pressed it :  "  Not  in  a  week,  or  a  month, 
or  a  year,  but  by  the  lives  of  many  souls, 
a  beautiful  thing  must  be  done." 

Since  the  electromagnetic  motor  con- 
sists essentially  of  means  whereby  a  con- 
tinuous rotary  motion  is  produced,  by  the 
combined  agency  of  an  electric  current 
and  a  magnet,  we  must  regard  the  first 
electric  motor  as  being  due  to  Faraday, 
who,  in  1821,  produced  the  apparatus 
shown  in  Fig.  8.  Here  a  permanent  steel 
bar  magnet  S  N,  is  fixed  in  a  cork,  which 
wholly  closes  the  lower  end  of  a  glass 
tube.  Enough  mercury  is  poured  in  to 


THE  TRANSMISSION    OF   POWER. 


75 


partly  cover  the  magnet.  An  electric  cur- 
rent is  caused  to  flow  in  the  neighborhood 
of  the  magnet,  through  a  movable  wire 
a  by  so  suspended  as  to  be  capable  of  rotat- 


FIG.  8.— THE  FIRST  ELECTROMAGNETIC  MOTOR. 

ing  its  lower  extremity  about  the  axis  of 
the  tube.  Under  the  combined  action  of 
the  current  and  the  magnet,  a  continu- 
ous rotary  motion  is  produced.  The 


76  THE   ELECTRIC    MOTOE   AND 

direction  of  this  motion  depends  upon  the 
direction  of  the  current,  as  well  as  on 
the  polarity  of  the  magnet ;  that  is  to  say, 
if  the  motion  be  right-handed,  or  clock- 
wise, when  the  current  is  in  one  direction 
through  the  wire,  it  will  be  left-handed, 
or  counter -clockwise,  if  the  direction 
of  current  be  reversed.  Similarly,  a  re- 
versal of  the  polarity  of  the  magnet,  will 
reverse  the  direction  of  the  motion.  The 
current  passes  through  the  conductor  in  the 
upper  cork  to  the  hook  a,  thence  through 
the  movable  wire  a  b,  and  out,  by  means 
of  the  mercury  and  the  lower  conductor. 

Let  us  inquire  into  the  cause  which  pro- 
duces the  electromagnetic  rotation  in  the 
case  of  the  simple  apparatus  shown  in  Fig. 
8.  To  do  this,  a  brief  examination  into 
the  elementary  principles  of  magnetism 
will  be  necessary. 


THE   TRANSMISSION   OF  POWER.  77 

We  have  experimental  knowledge  of  the 
fact  that  magnets  possess  the  power  of 
mutual  attraction  and  repulsion,  at  sensible 
distances  from  one  another.  It  would 
seem  at  first  sight,  that  magnets  possess 
the  power  of  producing  action  at  a  dis- 
tance, without  the  presence  of  any  inter- 
vening mechanism,  or  connecting  medium, 
but  this  doctrine  is  now  totally  discredited. 
Indeed,  it  can  be  shown  that  a  certain 
influence  emanates  from  the  magnet,  so 
that  a  magnet  is  a  piece  of  visible  matter 
accompanied  and  surrounded  by  an  in- 
visible influence,  which  must  be  regarded 
as  a  part  of  the  magnet  itself.  More- 
over, the  invisible  part  is  much  larger 
than  the  visible  part.  This  invisible 
part,  or  magnetic  field,  may  be  described 
as  a  region  traversed  by  an  emanation 
called  magnetic  flux.  The  existence  of 
this  flux  is  shown  either  by  the  action 


78  TI1K   ELECTRIC    MOTOR   AND 

exerted  upon  a  movable  compass  needle, 
when  brought  into  or  out  of  the  field, 
or  by  the  power  it  possesses  to  cause 
iron  filings  to  align  themselves  in  definite 
directions.  In  Fig.  9,  the  direction  of  the 
flux  paths  is  shown  by  means  of  the  group- 
ings of  iron  filings  which  have  been 
sprinkled  on  a  glass  plate  placed  over  a 
bar  magnet. 

Regarding  the  grouping  of  filings  as 
indicating  the  paths  of  magnetic  flux,  in 
the  plane  of  the  glass  plate,  it  will  be 
seen  that  curved  chains  of  filings  connect 
the  two  ends  JV,  and  $,  of  the  magnet, 
although  in  the  outlying  portions  of  the 
figure  the  interconnection  of  these  lines 
is  not  shown.  We  know,  however,  that  if 
the  figure  were  large  enough,  all  the  lines 
would  be  found  to  form  complete  closed 
paths.  Moreover,  it  can  be  shown  that 


80  THE   ELECTRIC   MOTOR   AND 

this  flux  not  only  occupies  the  space  out- 
side the  magnet,  but  also  penetrates  its 
substance,  and  that,  in  fact,  each  flux  path 
forms  an  endless  chain,  passing  through 
both  the  substance  of  the  magnet  and  the 
region  outside  the  magnet.  The  question 
naturally  arises  whether  the  magnetic  flux, 
or  at  least  that  part  of  it  which  lies  out- 
side the  magnet,  is  not  due  to  the  presence 
of  the  air  or  other  gross  medium  occupying 
this  space.  This,  however,  is  not  the  case, 
since  the  same  phenomena  occur  if  a 
vacuum  exists  outside  the  magnet,  that  is 
to  say,  if  the  magnet  be  enclosed  in  a 
chamber  exhausted  by  an  air-pump. 

There  is,  however,  a  medium  called  the 
universal  ether,  which,  as  can  be  shown, 
does  fill  this,  as  well  as  all  other  space. 
The  air-pump  is  unable  to  remove  this  me- 
dium, since  it  can  readily  pass  through  the 


THE   TRANSMISSION    OF   POWER.  81 

substance  of  glass  or  of  any  other  known 
material.  Although  the  exact  nature  of 
magnetic  flux  is  unknown,  yet  it  is  con- 
venient, for  purposes  of  explanation,  to 
assume  that  it  consists  of  a  streaming  motion 
of  the  ether ;  the  curved  lines,  occupied 
by  the  iron  filings,  corresponding  to  the 
stream-lines  or  lines  in  which  the  ether  is 
flowing. 

Since  a  flow  necessitates  a  motion  in  a 
definite  direction,  it  is  conventionally  as- 
sumed that  the  ether  streams;  i.  e.,  the 
magnetic  flux,  issue  from  the  magnet  at  its 
north  pole  ;  namely,  the  pole  which  would 
point  northwards,  if  the  magnets  were 
freely  suspended,  and  after  having  passed 
through  the  region  outside,  returns  into  the 
substance  of  the  magnet  at  its  south  pole, 
then  passing  through  the  substance  of  the 
magnet  and  reissuing  at  its  north  pole. 


82  THE   ELECTRIC    MOTOR   AND 

In  other  words,  a  magnet  may  be  regarded 
as  a  means  for  producing  a  streaming  mo- 
tion of  the  ether.  That  is  to  say,  an  ether 
streaming,  called  magnetic  flux,  moves  in 
closed  paths  or  circuits  around  the  mag- 
net. According  to  this  view,  a  bar  magnet 
acts  relatively  to  the  ether  whicli  per- 
meates and  surrounds  it,  in  the  same  way 
as  a  tube  placed  in  water  and  furnished 
with  a  pump  in  its  interior,  which  causes 
a  steady  stream  of  water  to  emerge  from 
the  tube  at  one  end,  and  to  re-enter  at  the 
other  end,  after  passing  through  the  sur- 
rounding liquid. 

What  we  call  the  magnetic  properties 
of  a  magnet  only  continue  to  exist  while 
the  magnet  is  producing  these  streaming 
^ther  motions ;  that  is,  while  it  is  producing 
magnetic  flux.  Anything  which  causes 
this  motion  to  cease,  causes  the  magnet  to 


THK  TRANSMISSION   OF  POWEK.  83 

lose  its  magnetic  properties,  and  anything 
which  enables  the  magnet  to  again  pro- 
duce this  flux,  will  enable  it  to  regain  its 
magnetic  properties.  Since  a  magnetized 
bar  of  hardened  steel  retains  its  magnet- 
ism for  an  indefinite  time,  we  assume  that 
it  possesses  the  power  of  indefinitely  pro- 
ducing the  ether  motion.  This  could  ex- 
ist without  loss  of  energy  if  we  assume,  as 
we  believe  to  be  true,  that  ether  is  a  fric- 
tionless  fluid. 

But  there  are  other  ways  of  setting  up 
streaming  ether  motion  ;  i.  <?.,  producing 
magnetic  flux  around  gross  matter.  If  an 
electric  conductor,  say  a  copper  wire,  has 
an  electric  current  passed  through  it,  the 
streaming  ether  motion  will  be  set  up  in 
concentric  circles  around  it.  The  presence 
of  this  circular  magnetic  flux  may  be 
shown  by  groupings  of  iron  filings  ob- 


84  THE   ELECTRIC   MOTOR   AND 

tained   in   a  similar    manner  to    that  de- 
scribed in  the  case  of  the  bar  magnet  and 


FIG.  10. — CIRCULAR   DISTRIBUTION    OF   FLUX    AROUND 
ACTIVE  CONDUCTOR. 


shown  in  Fig.  9.  Such  groupings  in  the 
case  of  an  active  wire  are  shown  in  Fig. 
10.  Here  a  horizontal  sheet  of  paper  has 


THE   TRANSMISSION    OF   POWER.  85 

been  placed  perpendicularly  to  a  vertical 
wire  while  an  electric  current  is  passing 
through  it. 

The  circular  magnetic  flux,  produced 
around  an  active  conductor  by  an  electric 
current,  like  the  flux  produced  by  a  per- 
manent bar  magnet,  has  a  definite  direction 
dependent  on  the  direction  of  current  in 
the  wire.  If  the  current  be  considered  to 
pass  through  the  wire  away  from  the 
observer,  the  magnetic  streamings  around 
the  conductor  will  have  the  same  direction 
as  that  of  the  hands  of  a  watch,  as  seen  by 
an  observer  facing  them.  Reversing  the 
direction  of  the  current  will  reverse  the 
direction  of  the  streamings.  The  stream- 
ings cease  as  soon  as  the  current  ceases. 
In  other  words,  the  magnetic  flux  around 
a  wire  is  dependent  upon  the  existence  of 
the  electric  current. 


86 


THE   ELECTRIC    MOTOtt   AND 


Fig.  11,  represents  diagrammatically  the 
magnetic  flux  passing  through  the  north 
pole  of  a  magnet  into  the  region  occupied 


FIG.  11.— DIAGRAMMATIC  KEPRESENTATION  OF  FLUX 
FROM  MAGNET,  SHOWN  IN  FIG.  8. 

by  the  wire  a  b,  of  Fig.  8.  If  no  current 
passes  through  the  wire,  this  magnetic  flux 
does  not  tend  to  produce  any  motion  in 
the  wire.  If,  however,  a  current  passes 
through  the  wire,  so  that  magnetic  flux 


THE  TRANSM«cr 


Y/8?^  P         <rV 


streams  around  it,  W^%  the  interactions  of 
the  two  magnetic  nS^re^pi^duce  a  t^-  c 
dency  to  move  the  conductor  across  the 
magnetic  flux  from  the  magnet,  and,  con- 
sequently, cause  the  wire  to  move  in  a 
circular  path  around  the  magnetic  pole. 
The  combination,  therefore,  of  an  active 
conductor  and  an  independent  magnetic  flux, 
constitutes  a  simple  electromagnetic  motor. 

As  is  well  known,  action  and  reaction 
are  always  equal  and  opposite,  so  that 
if  the  magnet  pulls  the  wire  around 
it  through  the  medium  of  the  inter- 
acting magnetic  fluxes,  the  wire  is  also 
producing  a  pull  on  the  magnet.  Conse- 
quently, if  the  wire  be  fixed  and  the  mag- 
net be  free  to  move  about  its  vertical  axis, 
it  may  be  made  to  rotate.  This  was 
actually  done  by  Faraday,  and  others  after 
him,  in  a  variety  of  apparatus. 


88  THE   ELECTRIC    MOTOR   AND 

Feeble  as  was  the  early  motor  of  Fara- 
day represented  in  Fig.  8,  yet  it  essentially 
embodied  the  principles  of  the  most  com- 
plex, powerful  and  efficient  electromag- 
netic motors  of  to-day,  and  a  comprehen- 
sion of  the  principles  involved  in  this 
simple  motor  gives  the  clue  to  the  action 
of  all  modern  motors. 

Fig.  12,  represents  a  modified  form  of 
the  early  motor  shown  in  Fig.  8.  Here  the 
electric  current  passes  from  the  base  of  the 
instrument  through  the  vertical  bar  mag- 
net A  J3.  The  metallic  support  D,  has 
pivoted  at  its  upper  extremity  a  delicately 
suspended  rectangular  conductor  E  F, 
which  has  its  two  free  ends  dipping  into 
a  circular  trough  of  mercury.  The  current 
divides  through  this  rectangular  loop,  pass- 
ing down  through  E  and  F.  Under  these 
circumstances,  a  continuous  rotary  motion 


THE  TRANSMISSION   OF   POWER. 


89 


of    the    rectangular    circuit  is    produced. 
This  apparatus  only  differs  from  the  pre- 


FIG.  12. — MODIFIED  FORM  OF  FARADAY  MOTOR. 


ceding  in  the  fact  that  two  wires  carry  the 
current  past  the  magnet,  instead  of  one. 


90  THE  ELECTRIC   MOTOR   AND 

The  fact  that  magnets  exhibit  mutual 
attractions  and  repulsions  for  one  another, 
was  known  from  the  dawn  of  magnetic 
science,  before  the  Christian  era,  and  the 
idea  of  obtaining  mechanical  motion  from 
magnets  naturally  originated  at,  perhaps, 
an  equally  early  date.  Continuous  motion 
was,  and  still  is,  impossible  with  perma- 
nent magnets,  for  the  reason  that  when  a 
magnet  has  attracted  either  a  piece  of  iron, 
or  another  magnet,  it  cannot  again  repel 
the  same  unless  its  magnetism  is  reversed, 
and  no  means  for  reversing  magnetism 
were  known,  until  the  magnetic  properties 
of  the  electric  current  were  discovered. 

Although  Faraday  was  the  first  to  pro- 
duce a  continuous  electromagnetic  rotation, 
and  is  justly  entitled  to  the  honor  of  pri- 
ority, yet  the  principle  which  he  adopted 
was  that  discovered  by  Oersted  in  1819. 


THE  TRANSMISSION   OF   POWER.  91 

Oersted's  discovery  not  only  showed  how  a 
magnet  could  be  produced  by  an  electric 
current,  but  also,  for  the  first  time  in  the 
history  of  science,  afforded  the  means  of 

reversing   at   will   the   direction   of   mag- 
es o 

netism,  and  thus  obtaining  a  continuous 
rotary  motion. 

Oersted  showed  that  when  an  electric 
circuit  was  completed,  the  circuit  thereby 
acquired  magnetic  properties,  and  pos- 
sessed the  power  of  attracting  or  repelling 
magnets  brought  into  its  vicinity,  the  ten- 
dency of  such  attraction  or  repulsion  being 
to  cause  a  magnet  to  set  itself  at  right 
angles  to  the  electric  current.  The  ap- 
paratus for  demonstrating  this  important 
principle  consists  essentially  of  a  wire  A  B, 
carrying  a  current,  and  brought  into  the 
vicinity  of  a  freely  suspended  horizontal 
compass  needle,  as  shown  in  Fig.  13.  As- 


92  THE   ELECTRIC    MOTOR   AND 


FIG.  13. — OERSTED'S  EXPERIMENT. 

suniing  the  magnet  to  be  placed  parallel 
to  the  conductor,  then  as  soon  as  the  cur- 


TJIE   TRANSMISSION   OF   POWER.  93 

rent  flows  through  the  wire,  the  needle 
will  be  deflected  and  will  tend  to  occupy  a 
position  at  right  angles  to  the  wire.  On 
the  cessation  of  the  current  in  the  wire, 
the  needle  returns  to  its  original  position 
under  the  influence  of  the  earth's  magnet- 
ism. The  direction  in  which  the  needle 
is  deflected  will  depend  upon  the  direction 
of  the  electric  current.  If  we  reverse  the 
direction  of  the  current  in  the  wire,  we  re- 
verse the  direction  of  deflection  in  the 
needle,  because  we  reverse  the  direction 
of  the  magnetic  flux  passing  around  the 
wire.  Also,  if  Ave  obtained  one  direction 
of  deflection  when  the  wire  is  held  above 
the  needle,  the  opposite  direction  of  deflec- 
tion will  be  obtained  when  the  wire  is  held 
beneath  the  needle.  The  cause  of  these 
phenomena  is  due  to  the  mutual  action  of 
the  flux  produced  by  the  needle  and  that 
produced  by  the  current  in  the  wire,  which 


94  THE  ELECTRIC   MOTOR  AND 

latter  disappears   on  the  cessation  of  the 
current. 

It  would  be  possible,  by  suitably  chang- 
ing the  direction  of  the  current,  to  set  up  a 
continuous  rotation  of  the  needle,  and,  in 
point  of  fact,  the  electric  motor  of  to-day 
consists  of  means  whereby  the  direction  of 
the  current  is  changed  at  such  times  as 
will  eft'ect  the  continuous  rotation  of  the 
magnet. 

Various  devices  were  suggested  by  Fara- 
day and  others  for  producing  continuous 
rotary  motion  by  electromagnetic  action. 
For  example,  in  1823,  Barlow  produced 
the  apparatus  shown  in  Fig.  14.  Here 
an  electric  current  passes  between  the 
centre  of  a  star-shaped  wheel  and  emerges 
at  its  lowest  point,  which  dips  in  a 
trough  of  mercury  included  in  the  circuit. 


THE  TBANSM 


<b 


PROPERTY  CF  ' 

OF  POWER.  9(T  ' 


A  horse-shoe 

magnetic  flux,  which  acting 

the   flux   produced   by   the  current 


FIG.  14. — BARLOW  WHEEL  MOTOR. 

through  the  star  wheel,  produces  a  con- 
tinuous rotation  of  the  latter.  Here  that 
part  of  the  wheel  lying  between  its  axis 


96  THE   ELECTRIC   MOTOR   AND 

and  the  point  dipping  into  the  mercury 
cup  corresponds  to  the  movable  wire 
shown  in  Figs.  8  and  13.  Instead,  however, 
of  the  same  wire,  or  wires,  being  continu- 
ously acted  on,  different  portions  or  teeth 
of  the  star  wheel  are  continuously  acted  on. 
As  before,  the  direction  of  motion  is  at 
right  angles  to  the  magnetic  flux  produced 
between  the  poles  of  the  horse-shoe. 

A  modification  of  Barlow's  wheel  was 
shortly  afterward  made  by  .  Sturgeon. 
Here  a  continuous  disc,  instead  of  a  star 
wheel,  was  employed  for  the  moving  part. 

None  of  the  early  motors,  so  far  de- 
scribed, were  capable  of  exerting  much 
activity,  but  such  activity  as  they  did 
exert,  was  derived,  as  in  the  case  of  all 
electric  motors,  from  the  source  supplying 
their  driving  current. 


THE   TRANSMISSION   OF   POWER.  97 

The  mechanical  activity  developed  in  a 
motor,  neglecting  frictioual  losses,  is  equal 
to  the  product  of  the  current  strength  in 
amperes,  passing  through  the  motor,  and 
the  C.  E.  M.  F.  in  volts  developed  by  the 
motor  through  its  rotation.  The  star  wheel 
represented  in  Fig.  14,  produces  a  C.  E.  M. 
F.  when  it  commences  to  turn,  and  to  this 
extent  the  rotating  motor  tends  to  act  as  a 
dynamo-electric  machine,  or  source  of  E. 
M.  F.  It  is  a  general  law,  discovered 
by  Faraday,  that  when  an  electric  con- 
ductor is  moved  across  a  magnetic  flux, 
an  E.  M.  F.  is  developed  in  the  con- 
ductor, whether  a  current  be  flowing 
through  the  conductor  or  not.  Conse- 
quently, when  the  spurs  of  the  star  wheel 
rotate  under  the  influence  of  the  force  pro- 
duced by  the  mutual  interaction  of  the 
fluxes  of  the  magnet  and  the  current, 
generally  called  the  electro-dynamic  force, 


98  THE   ELECTRIC   MOTOR   AND 

the  motion  of  the  spurs  through  the  flux 
produced  by  the  magnet,  establishes  in  the 
spurs  an  E.  M.  F.  which  is  counter,  or  op- 

^rrgpHE^^: ' 


FIG.  15. — FARADAY'S  Disc  DYNAMO. 

posed,  to  the  direction  of  the  current  in 
them.  The  product  of  this  C.  E.  M.  F. 
and  the.  current  strength,  is  equal  to  the 
activity  developed  by  the  wheel. 

Any  electric  motor  is,  therefore,  capable 
of  acting  as  a  dynamo,  if,  instead  of  being 


THE  TRANSMISSION   OF   POWER.  99 

driven  by  the  current,  it  is  moved  by 
mechanical  force.  In  fact  no  electromag- 
netic motor  can  operate  unless  it  be  cap- 
able, under  the  circumstances,  of  acting 
as  a  dynamo,  since,  otherwise,  the  motor 
w^ould  be  unable  to  absorb  or  take  activity 
from  the  circuit.  This  fact,  however,  was 
not  discovered  until  1831,  when  Faraday 
produced  what  was,  in  reality,  the  first 
dynamo-electric  generator  designed  for 
purposes  of  producing  electromotive  forces 
in  this  manner. 

Faraday's  early  apparatus  is  represented 
in  Fig.  15.  Here  a  disc  of  copper  is  so 
mounted  as  to  be  capable  of  rotation  be- 
tween the  poles  of  a  horse-shoe  magnet. 
Under  these  circumstances,  E.  M.  F's.  will 
be  set  up  in  the  disc,  between  its  centre 
and  edge,  and  these  E.  M.  F's.  may  be 
caused  to  produce  a  current  in  an  external 


100  THE   ELECTRIC   MOTOR   AND 

circuit  by  means  of  collectors,  one  con- 
nected with  the  axis  of  the  disc,  and  the 
other  with  its  periphery.  The  direction 
of  these  E.  M.  F's.  will  depend  both  on 
the  direction  of  rotation  of  the  disc  and  on 
the  position  of  the  poles  of  the  magnet. 
Reversing  either  the  polarity  of  the  mag- 
net, or  reversing  the  direction  of  rotation, 
will  reverse  the  direction  of  the  E.  M.  F. ; 
and,  consequently,  the  direction  of  the  cur- 
rent supplied  to  the  external  circuit,  but  it 
always  happens  that  the  direction  of  the 
E.  M.  F.  which  is  developed  in  such  a 
machine,  or  indeed,  in  any  motor,  when 
rotated  by  electromagnetic  forces  supplied 
by  a  current,  is  opposed  or  counter  to  the 
direction  of  the  driving  current. 

If,  therefore,  instead  of  rotating  the 
wheel  shown  in  Fig.  16,  it  be  left  at 
rest,  and  an  electric  current  from  an 


THE   TRANSMISSION    OF    POWER. 


101 


external  source  be  sent  through  it  in  the 
direction  of  the  arrows,  then,  under  the 
influence  of  the  electro-dynamic  force  a 


a 


FIG.  16. — JACOBI'S  ELECTRIC  MOTOR.     V 

rotation  of  the  wheel  will  be  produced  in 
the  opposite  direction  to  that  represented 
by  the  arrow. 


102  THE   ELECTRIC   MOTOR   AND 

Without  attempting  to  trace  fully  the 
gradual  developments  of  the  electric 
motor,  it  suffices  to  say  that  one  of  the 
earliest  practical  motors  was  produced  by 
Jacobi  in  1834,  and  perfected  in  1838. 
This  motor  is  interesting  from  a  historical 
standpoint,  from  the  fact  that  in  its  im- 
proved form  it  was  employed  for  the  pro- 
pulsion of  a  boat  on  the  river  Neva,  in 
1838.  In  this  case  the  motor  was  driven 
by  a  voltaic  battery. 

Jacobi's  electric  motor  is  represented 
in  Fig.  16.  Here  two  vertical,  parallel 
frames  of  wood,  support  a  number  of 
horse-shoe  electromagnets  /  i.  e.y  horse-shoe- 
shaped  iron  cores,  wound  with  insulated 
copper  wire.  Such  a  magnet  acquires  its 
magnetism  almost  instantly  on  the  passage 
of  an  electric  current,  and  almost  instantly 
loses  it  when  the  current  ceases.  It  is 


THE  TRANSMISSION   OF   POWER.          103 

thus  capable  of  becoming  magnetized  and 
demagnetized  with  great  rapidity.  The 
magnets  in  the  outer  frame  were  kept  per- 
manently excited  by  a  steady  electric  cur- 
rent from  the  battery.  Between  these 
frames  a  wooden  star  wheel  was  supported 
on  the  axis  a  a.  In  the  spurs  of  this 
star  wheel  were  mounted  the  six  sets 
of  electromagnets  s,  s,  s,  s,  s,  s.  The  in- 
sulated wires  leading  to  these  bar  mag- 
nets were  connected  with  the  commutating 
apparatus  c,  in  such  a  manner  that  the 
brushes  A,  7i,  resting  on  the  commutator 
disc,  supplied  an  electric  current  to  the 
rotating  magnets  from  the  battery.  As 
soon  as  the  current  was  supplied  to  the 
star  wheel  magnets,  they  attracted  the 
fixed  electromagnets  in  their  vicinity  and 
pulled  around  the  star  wheel  to  meet 
them,  but  just  as  they  came  opposite  to 
one  another,  the  rings  6Y,  reversed  the  cur- 


104  THE   ELECTRIC    MOTOR   AND 

rent  passing  into  the  moving  magnets, 
thus  permitting  the  magnets  in  the  frame 
to  repel  them,  and  the  magnets  next  in 
succession  to  attract  them.  In  this  way 
a  continuous  rotary  motion  was  produced. 

The  first  electric  motor  produced  in  the 
United  States  was  that  of  Davenport,  who 
in  1837,  designed  an  electromagnetic  motor 
in  which  permanent  magnets,  placed  on  a 
fixed  frame,  attracted  and  were  attracted  by 
electromagnets  placed  on  a  moving  frame. 
Davenport  perfected  his  motor  to  an  ex- 
tent which  enabled  him  to  apply  it  to  the 
driving  of  a  printing  press,  and  to  the 
operation  of  a  small  model  of  a  circular 
railway,  which  he  exhibited  at  Springfield, 
Mass. 

The  principal  of  the  operation  of  the 
Jacobi  motor  may,  perhaps,  be  better  un- 


THE   TRANSMISSION   OF   POWER. 


105 


derstood  by  an  examination  of  a  motor  de- 
signed by  Ritchie,  which  operates  on  the 


FIG.  17.— RITCHIE'S  MOTOR. 


preceding    principles.     Ritchie's   motor  is 
shown  in  Fig.  17.     Here  a  movable  elec- 


106  THE   ELECTKIC   MOTOR  AND 

tromagnet  A  J3,  is  caused  to  continuously 
rotate  under  the  mutual  interaction  of  its 
flux  and  the  flux  produced  by  a  perma- 
nent magnet  N  8.  Suppose  the  electro- 
magnet to  occupy  at  any  instant  the  posi- 
tion shown  in  the  figure,  and  suppose, 
moreover,  that  the  current  be  flowing 
through  the  coils  of  the  electromagnet  in 
such  a  direction  as  to  produce  a  south  pole 
at  A,  and  a  north  pole  at  £,  and  that  the 
permanent  magnet  has  its  north  pole  at  JVJ 
and  its  south  pole  at  /X  Then  an  attrac- 
tion will  take  place  between  the  poles  of 
the  permanent  and  the  electromagnet, 
which  will  cause  the  latter  to  be  moved 
around  its  axis  in  the  direction  of  the 
arrow. 

If  the  current  continued  to  flow  steadily 
through  the  coils  of  the  electromagnet,  the 
movement  of  the  magnet  would  cease  as 


OflWWlH.  t'i   UOl/    Cl 


THE  TKANSMIS 

soon  as  its  poles  came 
poles  of  the  permanent 
moment,  by  means  of  the  commutator  (7, 
the  current  is  reversed  in  the  electromagnet 
by  reversing  its  polarity.  Under  these 
conditions,  aided  by  the  momentum  of  the 
moving  electromagnet,  repulsion  is  pro- 
duced between  the  poles  N~  and  A,  and 
the  rotation  is  continued  in  the  same 
direction  until  the  pole  A,  of  the  electro- 
magnet comes  over  the  pole  /Sy,  of  the  per- 
manent magnet,  when  the  commutator 
again  reverses  the  direction  of  the  current. 
On  this  account  the  pull  will  not  be  uni- 
form in  such  a  machine  at  all  positions  of 
the  electromagnet.  Moreover,  if  the  ma- 
chine were  to  stop  with  its  electromagnetic 
poles  vertically  over  the  permanent  mag- 
netic poles,  it  would  require  a  mechanical 
motion  before  the  current  could  again  pro- 
duce continued  rotation. 


108 


THE   ELECTRIC   MOTOR  AND 


The   next  important  development,    his- 
torically,   was   that   made  by  Elias,  who 


FIG.  18. — ELIAS'  MOTOR. 


in  1842  designed  the  motor  shown  in 
Fig.  18.  Here,  two  coaxial  iron  rings  are 
supported  in  the  same  vertical  plane.  The 


THE   TRANSMISSION    OF   POWER.  109 

outer  ring  is  fixed  and  the  inner  ring  is 
movable  about  its  axis.  In  this  form  of 
motor  it  will  be  noticed  that,  instead  of 
employing  a  permanent  magnet  for  the 
fixed  magnet,  an  electromagnet  is  em- 
ployed. This  marks  a  considerable  ad- 
vance in  the  art ;  for,  while  it  is  now 
obvious  that  a  fixed  electromagnet  is  equiv- 
alent to  a  fixed  permanent  magnet,  yet 
at  the  early  date  of  which  we  are  speaking, 
this  was  by  no  means  an  obvious  matter. 
In  fact,  the  earlier  motors  were  constructed, 
as  we  have  seen,  with  permanent  magnets, 
while  the  modern  motor,  when  of  any  con- 
siderable size,  is  invariably  provided  with 
electromagnets. 

Broadly,  then,  an  electromagnetic  motor 
consists  of  two  parts,  in  one  of  which  the 
magnetic  flux  is  fixed,  and  in  the  other  the 
magnetic  flux  is  movable,  being  changed 


110  THE   ELECTRIC    MOTOR   AND 

at  suitable  intervals  by  the  action  of  a 
commutator.  The  fixed  part  is  called  the 
field  magnet,  and  the  magnetically  moving 
part  the  armature.  In  nearly  all  cases  it 
is  the  magnetically  moving  part  which 
rotates,  the  field  magnets  being  usually 
fixed  and  the  armature  moving;  but,  as 
we  have  seen,  this  is  not  essential,  since 
action  and  reaction  are  always  equal  and 
opposite,  and  we  may  have  the  magnetically 
fixed  part  rotary,  and  the  magnetically 
moving  part  at  rest.  In  order  conven- 
iently to  distinguish  between  the  mechan- 
ically moving  and  the  magnetically  moving 
parts,  the  name  stator  is  sometimes  applied 
to  the  part  which  is  mechanically  fixed, 
and  the  name  rotor  to  the  part  which 
rotates,  no  matter  what  their  magnetic 
condition  may  be. 

Referring   again   to   Fig.    18,  the  outer 


THE  TRANSMISSION   OF  POWER.  Ill 

fixed  ring  constitutes  the  field,  and  the 
inner  movable  ring  the  armature.  Both 
field  and  armature  are  so  wound  with  coils 
of  insulated  wire  as  to. produce  six  poles 
at  equal  angular  distances  around  their 
circumference,  adjacent  poles  being  of 
opposite  polarity,  as  indicated  by  the 
letters  N,  S,  'N,  S,  N,  S,  in  the  field,  and 
?i,  s,  Uj  s,  n,  s,  in  the  armature. 

In  this  early  form  of  motor,  instead  of 
employing  the  same  current  to  excite  both 
the  field  and  armature,  a  separate  current 
was  employed  to  excite  the  field  magnets, 
or,  as  it  is  now  expressed,  this  was  a 
separately -excited  motor.  The  current  pass- 
ing through  the  armature  was  supplied 
through  the  terminals  7?,  .B'.  The  com- 
mutator G,  which  was  so  arranged  that  the 
brushes  7?,  72,  resting  on  the  commutator 
segments,  supplied  current  through  the 


THE   ELECTRIC    MOTOR   AND 

armature  by  the  wires  f,f,  in  a  direction 
which  produced  the  poles  n,  s,  n,  s,  n,  s, 
when  the  armature  occupied  the  position 
indicated  in  the  figure.  Here  the  north 
poles  in  the  armature  attract  the  south 
poles  of  the  field,  and  the  south  poles  of 
the  armature  attract  the  north  poles  of  the 
field,  in  such  a  manner  as  to  cause  the 
armature  to  be  pulled  around  clockwise, 
or  in  the  direction  of  the  arrow.  As  soon 
as  the  poles  in  the  armature  come  beneath 
the  field  poles,  the  armature  poles  are 
reversed  by  the  brushes  changing  the  seg- 
ments upon  which  they  rest  at  the  commu- 
tator, and  thus  reversing  the  direction  of 
current  and  the  polarity  of  the  armaturey 
so  that,  aided  by  momentum,  the  arma- 
ture poles  repel  the  field  poles  nearest 
to  them,  and  attract  those  ahead  of 
them,  thus  maintaining  a  continuous  rota- 
tion. 


THE  TRANSMISSION   OF   POWER. 

This  early  type  of  machine  must  be 
regarded  as  exhibiting  a  considerable  ad- 
vance over  its  predecessors,  and  would, 
indeed,  with  comparatively  small  modifica- 
tion, make  a  motor  approximating  to  the 
type  of  motors  in  modern  use.  It  belongs 
to  the  type  of  machine  now  well  estab- 
lished, called  a  multipolar  machine,  since 
it  has  more  than  two  poles.  It  is,  in  fact, 
a  sextipolar,  or  six-pole  machine. 

The  type  of  machine  shown  in  Fig.  10, 
was  constructed  by  Froment  in  1845. 
Here,  as  will  be  seen  from  an  examination 
in  the  figure,  a  continuous  rotatory  motion 
is  obtained  by  means  of  the  action  of 
electromagnets  upon  pieces  of  soft  iron, 
called  armatures,  attached  to  the  periph- 
ery of  a  movable  wheel.  The  current 
is  supplied  from  the  battery  B,  to  the 
motor  through  the  terminals  T,  T,  and 


114  THE   ELECTRIC    MOTOR   AND 

through  the  commutator  C\  to  the  magnets 
M  M  in  such  a  manner  that  when  the 


FIG.  19. — FROMENT'S  MOTOR. 

circuit  is  completed,  the  magnets  M,  M, 
attract  the  soft  iron  bars  A,  A,  A,  and 
pull  the  armature  around,  say  in  a  clock- 
wise direction.  As  soon  as  the  bars 
A,  Ay  Ay  are  opposite  to  the  magnet 


THE  TRANSMISSION    OF   POWER.          115 

poles,  the  current  is  cut  oft'  at  the  commu- 
tator, the  armature  continuing  iu  rotation 

o 

by  its  momentum  until  the  bars  are  ready 
to  be  attracted  by  the  next  succeeding 
magnets,  when  the  circuit  is  closed  at  the 

commutator.       Successive     magnetic     im- 

~ 

pulses  are  thereby  created,  which  result 
in  a  continuous  rotatory  motion  of  the 
armature.  A  number  of  motors,  of  dif- 
ferent designs,  but  based  on  this  general 
principle,  were  constructed  by  Froment. 

Between  1845  and  the  present  date, 
very  many  electromagnetic  motors  have 
been  designed.  With  the  limited  space 
at  our  disposal  we  will  not  attempt  any 
farther  to  trace  the  early  history  of  the 
electric  motor,  except  to  give  a  description 
of  a  very  excellent  form  of  early  motor 
designed  by  Pacinotti  in  1861,  and  repre- 
sented in  Fig.  20.  Here  the  armature  A, 


116  THE   ELECTRIC   MOTOR   AND 

is  mounted  on  a  vertical  axis  between  the 
poles  of  the  electromagnets  J/i,  and  M& 
which  constitute  the  field  magnets.  The 
current  is  supplied  through  the  terminals 
2J,  and  T%,  say  from  T±  to  the  magnets  J/i, 
and  M&  thence  through  the  commutator 
apparatus  6Y,  to  the  armature,  leaving  by 
the  terminal  jT2.  The  field  magnets  M^ 
and  J/2»  are,  therefore,  excited  in  series 
with  the  armature,  so  that  the  machine 
is  said  to  be  series-wound. 

The  armature  consists  of  an  iron  ring, 
wound  at  intervals  with  coils  of  insulated 
wire  connected  with  the  commutator,  in 
such  a  manner  as  to  produce  poles  in  the 
armature  between  the  polar  projections  N 
and  8,  of  the  field  magnets.  The  armature 
turns  so  as  to  bring  its  poles  directly 
opposite  to  the  field  poles.  As  it  moves, 
however,  the  poles  in  the  armature  are 


118  THE   ELECTRIC   MOTOR. 

shifted  by  the  action  of  the  commutator, 
so  that  a  continuous  rotation  takes  place. 
Like  all  electromagnetic  motors  this 
machine,  when  independently  driven  as 
a  dynamo,  is  capable  of  producing  an 
E.  M.  F.  provided  the  field  magnets  are 
suitably  excited.  The  handle  and  disc 
shown  behind  the  motor,  were  intended  for 
the  purpose  of  demonstrating  this  fact. 


CHAPTER  V. 

ELEMENTARY  THEORY  OF  THE  MOTOR. 

HAVING  thus  briefly  traced  some  of  the 
early  history  of  electric  motors,  we  will 
proceed  to  the  theory  of  their  operation.- 
Although  this  theory  could  readily  be 
deduced  from  any  of  the  motors  we 
have  considered,  yet  it  will,  perhaps,  be 
preferable  to  base  it  upon  a  more  modern 
type  of  motor,  such  as  the  machine  shown 
in  Fig.  21.  This  machine  is  of  the  bipolar 
type.  It  has  two  field  poles  -N  and  S, 
produced  by  the  magnetizing  coils  Jt/,  M. 
Between  these  poles  the  armature  A,  is 
free  to  revolve.  The  commutator  C,  and 
pulley  P,  are  carried  by  the  armature  shaft. 


119 


120  THE   ELECTRIC   MOTOR   AND 

The  brushes  £,  J9,  rest  upon  the  com- 
mutator, and  supply  the  current  to  the 
armature  from  the  main  terminals  T,  T, 


FIG.  21. — BIPOLAR  ELECTRIC  MOTOR. 

in  such  a  manner  as  to  produce  in  it  two 
poles,  n  and  s,  midway  between  the  poles 
N  and  S,  of  the  field  magnet.  The  arma- 
ture is,  therefore,  pulled  around  in  the 


THE   TRANSMISSION 

direction  of  the  arrow, 

the  current  entering  the 

muted  in  such  a  manner  as  to  maintain  the 

armature  poles  at  their  positions    in    the 

vertical  plane. 

The  power  of  an  electric  motor  depends 
upon  two  things;  viz., 

(1)  Upon  the  pull  it  exerts  at  the  cir- 
cumference of  its  pulley,  and, 

(2)  Upon  the  speed  at  which  it  runs. 
The  greater  the  pull,  and  the  greater  the 

speed  at  which  that  pull  is  delivered,  the 
greater  the  activity  of  the  motor. 

Since  it  is  the  electro-dynamic  force 
\vhich  causes  the  rotation  of  a  motor,  it  is 
clear  that  the  pull,  which  will  be  exerted 
at  the  circumference  of  the  pulley,  will 
vary  with  the  diameter  of  the  pulley.  It 
is  customary  to  speak  of  the  effect  of  this 


122 


THE   ELECTRIC    MOTOR    AND 


electro-dynamic  force  as  the  torque,  a  word 
derived  from  the  Latin  verb  to  twist.  Sup- 
pose the  electro-dynamic  force  of  the  motor 


w 


FIG.  22.— TORQUE  EXERTED  UPON  SHAFTS  BY  WEIGHTS 
SUSPENDED  OVER  A  PULLEY. 

were  capable  of  exerting  a  twist  or  torque 
about  the  axis  of  the  armature,  represented 
by  the  pull  of  100  pounds'  weight,  sus- 
pended over  a  pulley  P,  Fig.  22,  1  foot  in 
radius ;  then  it  will  be  evident  that  if  the 


THE   TRANSMISSION    OF   POWER,          123 

pulley  were  exchanged  for  one  4  feet  in 
radius,  as  shown  at  P',  in  the  same 
figure,  the  motor  would  only  be  capable 
of  lifting  a  weight  of  25  pounds  sus- 


FIG.  23.— EQUILIBRIUM  OP  Two  EQUAL  AND  OPPOSITE 
TORQUES. 

pended  over  this  pulley;  or,  a  torque 
of  100  pounds  at  a  radius  of  one  foot 
is  the  same  as  that  exerted  by  25  pounds 
at  a  radius  of  four  feet.  In  fact  it  is 
clear  that  if  the  two  pulleys  P  and  P', 


124 


THE   ELECTRIC    MOTOR   AND 


were  mounted  side  by  side  011  the  same 
shaft,  and  the  weights  W  and  W\  sus- 
pended from  their  peripheries  on  opposite 
sides,  the  torques  exerted  would  be  equal 


FIG.  24.— DIAGRAMS  OF  TORQUE. 

and  opposite,  or  the  shaft  would  remain  in 
equilibrium,  as  in  Fig.  23. 

Fig.  24,  represents  a  torque  of  20  pounds- 
feet,  acting  about  the  axis  of  each  of  the 
three  pulleys  P±  _P2,  and  P3 ;  for,  at  P^  we 
have  a  force  of  40  pounds'  weight  acting 


THE   TRANSMISSION    OF   POWER.          125 

at  a  radius  of  1/2  a  foot  —  20  pounds-feet ; 
at  P%,  we  have  a  force  of  20  pounds'  weight 
acting  at  a  radius  of  1  foot  =  20  pounds-feet ; 
and,  at  P3,  we  have  a  force  of  10  pounds' 
weight  acting  at  a  radius  of  2  feet  =  20 
pounds-feet.  It  is  evident,  that  the  torque 
of  a  motor  does  not  imply  any  particular 
size  of  the  pulley  on  the  motor ;  for,  if  a 
pulley  of  large  diameter  be  employed,  the 
force  at  its  periphery  will  be  comparatively 
small,  while  if  a  pulley  of  small  diameter 
be  employed,  the  force  at  its  periphery 
will  be  comparatively  great. 

In  the  same  way,  the  amount  of  work 
which  a  motor  exerting  a  given  torque  will 
perform,  during  one  complete  revolution 
of  its  armature  or  pulley,  does  not  imply 
any  particular  diameter  of  the  pulley ; 
but,  if  the  pull  to  be  exerted  is  given, 
then  the  limiting  diameter,  at  which 


126  THE   ELECTRIC   MOTOR   AND 

that  pull  can  be  exerted  is  known.  Thus 
if  a  motor  exerts  a  torque  of  20  pounds- 
feet  independently  of  the  speed  at  which 
it  runs,  and  the  pulley  Plf  of  Fig.  24  be  em- 
ployed on  its  shaft,  with  a  radius  of  half  a 
foot,  the  motor  will  just  be  capable  of  lifting 
40  pounds'  weight  on  the  periphery  of  the 
pulley ;  and,  in  one  complete  revolution, 
the  pulley  will  raise  this  weight  through  a 
distance  equal  to  its  own  circumference; 
namely,  to  1/2  X  6.2832  =  3.1416  feet,  and 
will,  therefore,  do  an  amount  of  work  equal 
to  3.1416  x  40  =  125.66  foot-pounds  = 
170.4  joules.  If,  however,  the  pulley  jP2,  be 
employed,  with  a  radius  of  one  foot,  the 
motor  will  just  lift  a  weight  of  20  pounds 
over  its  periphery;  and,  in  one  complete 
revolution,  will  do  an  amount  of  work  equal 
to  6.2832  feet  x  20  pounds  =  125.66  foot- 
pounds =  170.4  joules.  Finally,  if  the 
pully  P3j  be  employed,  the  weight,  which 


THE  TRANSMISSION   OF   POWER.          127 

the  motor  \vill  lift  over  its  periphery,  will  be 
just  10  pounds,  and  its  circumference  being 
2  X  6.2832  =  12.5664  feet,  the  amount  of 
work  done  by  the  motor  in  one  revolution 
will  be  12.5664  x  10  =  125.66  foot-pounds 
=  170.4  joules;  or,  as  we  have  already 
stated,  the  work  done  by  a  given  torque  in  a 
given  number  of  revolutions  is  independent 
of  the  radius  of  the  pulley.  If  the  pulley 
be  large,  the  weight  raised  will  be  small, 
but  the  lift  per  revolution  great,  while,  if  the 
pulley  be  small,  the  weight  raised  will 
be  great,  but  the  lift  per  revolution  small. 
On  the  other  hand,  if  the  weight  to  be 
lifted  be  known,  the  size  of  the  pulley 
will  be  limited  by  the  torque  of  the  motor. 
Thus,  a  motor  of  40  pounds-feet  torque 
could  not  lift  a  weight  of  5  pounds  over 
a  pulley  more  than  8  feet  in  radius. 

The  activity  of  a  motor,  being  the  work 


128 


THE   ELECTRIC    MOTOR   AISTD 


done  per  second,  will  be  equal  to  the  prod- 
uct of  the  torque  and  6.2832  times  the 
number  of  revolutions  per  second.  Thus,  if 


FIG.  25. — MAGNETIC  CIRCUIT  OF  MOTOR  REPRESENTED 
IN  FIG.  21. 

a  motor,  exerting  a  steady  torque  of  50 
pounds-feet,  runs  at  1,200  revolutions  a 
minute,  or  20  revolutions  per  second,  the 
activity  may  be  reckoned  directly  as  50  X 
6.2832  X  20  =  6283.2  foot-pounds  per 


THE   TRANSMISSION   OF   POWER.          129 

second.  A  similar  calculation  will  show 
that  the  activity  of  the  motor  would  be 
the  same  with  pulleys  P2  and  P3.  For, 
although  with  the  larger  pulleys  the  per- 
ipheral speed  in  feet  per  second  would  be 
greater,  yet  the  weights  they  would  raise 
would  be  correspondingly  smaller. 

The  torque  exerted  by  a  motor  is  the 
most  convenient  quantity  for  considering 
and  discussing  its  mechanical  power,  anjd 
we  will  now  proceed  to  consider  how  this 
torque  varies  with  the  electrical  conditions 
in  the  motor. 

To  do  this  it  will  be  necessary  to  con- 
sider the  magnetic  flux  passing  through 
the  magnetic  circuit  of  the  motor.  Fig.  25 
represents  diagrammatically  the  magnetic 
circuit  of  the  motor  shown  in  Fig.  21. 
Here  the  armature  A,  is  situated  between 


130  THE   ELECTRIC   MOTOR   AND 

pole  pieces  JV  and  &,  and  is  separated  from 
them  by  two  annular  air-gaps,  one  between 
the  armature  and  JV,  and  the  other  between 
the  armature  and  8.  The  magnetic  flux, 
which  passes  through  this  magnetic  cir- 
cuit, is  produced  by  the  magnetizing  coils 
which  are  wound  upon  the  iron  cores, 
<7,  C'. 

We  have  seen  that  the  current  strength 
produced  by  an  electric  source  depends 
upon  the  E.  M.  F.  of  the  source,  and  the 
resistance  of  its  circuit.  In  the  same  way, 
in  the  magnetic  circuit,  the  magnetic  cur- 
rent, or  magnetic  flux,  depends  upon  the 
magneto-motive  force  of  the  source,  and 
upon  the  magnetic  resistance  of  the  circuit ; 
or,  just  as  we  had, 

T7S        ~\jT       TT1 

Electric  current  or  flux  =  ™— 


Electric  Resistance 

so  here, 

M.  M.  F. 

Magnetic  current  or  flux  =  =r= -. — „ — r— 

Magnetic  Resistance. 


THE   TRANSMISSION   OF   POWER.          131 

Magnetic  flux  is  estimated  in  units  of 
magnetic  flux,  commonly  called  webers.  A 
large  motor  may  Lave  a  total  magnetic  flux 
of  millions  of  webers,  while  a  small  motor, 
suitable  for  driving  a  table  fan,  may  Lave 
a  total  flux  in  its  circuit  of  only  a  few 
thousand  webers. 

•  The  unit  of  magneto-motive  force,  usually 
written  M.  M.  F.,  is  commonly  called  the 
gilbert,  and  is  the  M.  M.  F.  which  would  be 
produced  by  a  current  of  0.7958  amperes, 
flowing  through  one  turn  of  wire.  In  other 
words,  a  current  of  one  ampere,  passing 
through  one  turn  of  wire ;  i.  e.,  one  ampere- 
turn,  produces  an  M.  M.  F.  of  1.257  gilberts. 
The  M.  M.  F.  of  a  coil  of  wire  is,  therefore, 
proportional  to  the  number  of  ampere- 
turns  in  it.  If  each  of  the  coils  on  the 
magnets  of  Figs.  21  and  25,  have  2,000 
turns,  and  carries  a  steady  current  of  5 


132  THE  ELECTRIC   MOTOR  AND 

amperes,  then  the  M.  M.  F.  of  the  coils 
will  be  5  X  2,000  =  10,000  ampere-turns 
=  12,570  gilberts  in  each  coil,  or  20,000 
ampere-turns,  and  25,140  gilberts  in  the 
complete  circuit. 

The  amount  of  flux  which  will  be  pro- 
duced by  this  M.  M.  F.  will  depend  upon 
the  magnetic  resistance  of  the  circuit ;  that 
is,  on  the  magnetic  resistance  in  the  iron 
of  the  cores  C  O',  the  yoke  Y,  the  pole- 
pieces  JVand  S,  the  iron  armature  core  A, 
and  the  air-gaps,  on  each  side  of  the  arma- 
ture, through  which  the  flux  passes. 

The  magnetic  resistance  of  a  circuit, 
usually  called  its  reluctance,  is  measured 
in  units  of  magnetic  resistance  commonly 
called  oersteds.  The  oersted  is  the  resist- 
ance offered  by  a  centimetre  cube  of  air, 
that  is  to  say,  it  is  equal  to  the  magnetic 


THE   TRANSMISSION    OF   POWEK.          133 

resistance  wliicli  a  colunm  of  air  offers 
when  it  has  a  length  of  one  centimetre  and 
a  cross-sectional  area  of  one  square  centi- 
metre. As  in  the  case  of  an  electric  cir- 
cuit, the  electric  resistance  increases  with 
the  length  of  the  circuit  and  decreases  with 
the  area  of  cross-section,  so  in  the  mag- 
netic circuit,  the  magnetic  resistance  or 
reluctance  increases  with  the  length,  and 
decreases  with  the  area  of  cross-section. 
Thus,  if  each  of  the  air-gaps  in  Fig.  25  is 
one  centimetre  long  in  the  direction  of  the 
magnetic  flux,  and  has  an  effective  cross- 
sectional  area,  called  polar  area,  of  1,000 
square  centimetres,  then  the  reluctance 

of   each    air-gap  will   be    =    0.001 

oersted,  and  the  total  reluctance  in  the 
air  0.002  oersted. 

The   reluctance   of   most   substances  is 


134  THE   ELECTRIC    MOTOR   AND 

practically  the  same  as  that  of  air,  and  is 
not  affected  by  the  quantity  of  flux  which 
passes  through  it.  In  the  case  of  iron, 
however,  the  magnetic  reluctance  is  very 
small  as  compared  with  air,  provided  the 
magnetic  flux  through  it  is  not  very  dense. 
When,  however,  the  magnetic  flux  is  very 
powerful,  so  that  a  great  number  of  webers 
pass  through  each  square  inch  of  cross- 
sectional  area,  the  iron  is  said  to  become 
magnetically  saturated,  and  then  offers  a 
greatly  increased  reluctance.  Thus,  at  a 
density  of  5,000  webers-per-square-centi- 
metre,  which  is  commonly  called  a  density  of 
5,000  gausses,  the  gauss  being  the  unit  of 
magnetic  density,  the  reluctance  of  a  cubic 

centimetre  of  iron  is   only  about         —  th 

2,000™ 

that  of  the  reluctance  of  a  cubic  centimetre 
of  air ;  but  at  a  density  of  1 6,000  webers- 
per-square-centirnetre, or  at  16,000  gausses; 


THE   TRANSMISSION    OF   POWER.          135 

i.  e.y   16   Iciloyavsses,  the  reluctance  of   a 
cubic  centimetre  of  soft  iron  may  be 


that  of  air.  The  specific  reluctance  of  iron 
in  terms  of  air;  i.  e.,  its  reluctivity,  varies 
with  the  density  of  the  flux  passing  through 
it,  and  also  with  the  quality  of  the  iron. 
The  density  of  flux  usually  employed  in 
motors  containing  cast  iron  in  their  magnetic 
circuit,  is  not  more  than  8,000  or  9,000 
gausses;  while  in  motors,  employing  soft 
wrought  iron  or  soft  steel,  the  density 
which  may  be  employed  is  12,000  to  15,000 
gausses.  There  is,  therefore,  a  considerable 
magnetic  advantage  in  employing  soft  iron, 
or  cast  steel,  in  place  of  ordinary  gray  cast 
iron,  in  the  magnetic  circuits  of  dynamos 
and  motors,  since  the  former  have  a  much 
lower  magnetic  resistance. 

If,  in  Fig.  25,  we  assume  that  the  total 


136  THE    ELECTUIC    MOTOR   AND 

reluctance  of  the  iron  of  the  magnetic 
circuit  be  0.003  oersted,  then  the  total 
reluctance  in  the  circuit  composed  of  iron 
and  air,  will  be  0.003  +  0.002  =  0.005 
oersted,  and  the  magnetic  flux  passing 
through  the  circuit  will  be 

25,140  gilberts 

^—  -  --=  0,028,000  webers. 

O.OOo  oersteds 

Fig.  25,  shows  that  some  of  the  mag- 
netic flux  does  not  pass  through  the 
armature,  but  through  the  air  on  each  side 

o 

of  the  field  magnets.  All  such  stray  flux 
not  passing  through  the  armature  is  use- 
less for  the  purpose  of  rotating  the  arma- 
ture, and  is,  therefore,  called  leakage  flux. 
Magnetic  leakage  necessarily  occurs  because 
there  is  no  known  magnetic  insulator.  An 
electric  current  can  be  restricted  by  the  use 
of  insulators  to  the  conductors  conveying  it, 
such  as  air,  dry  wood,  rubber,  etc.,  but 


PROPERTY  CF 


THE  TRANSMISSION  >fo0WKR.          137 


dry  wood,  rubber,  glass 
materials  except  the  magnetic  nietals7cor£ 
duct  magnetic  flux  with  equal  facility ;  i.  e., 
have  practically  the  same  reluctivity.  Con- 
sequently, some  of  the  magnetic  flux  pro- 
duced in  the  circuit  by  the  M.  M.  F.  of  the 
field  coils,  will  pass  uselessly  through  the 
surrounding  air.  The  useful  magnetic 
flux  is  that  which  passes  through  the 
armature.  The  leakage  can  be  reduced  by 
diminishing  the  reluctance  in  the  armature 
circuit  relatively  to  the  reluctance  of  the 
leakage  paths  surrounding  the  cores. 

If  the  cross-section  of  the  armature  A., 
be  known  in  square  inches,  the  total  useful 
flux  passing  through  it  may  be  readily 
estimated  ;  for,  it  is  usual  to  employ  in  the 
armature  core  a  flux  density  of,  approxi- 
mately, ten  kilogausses.  This  is  a  density 
well  below  saturation,  and,  since  there  are, 


138  THE   ELECTRIC    MOTOR   AND 

6.4516  square  centimetres  in  a  square  inch, 
there  will  be,  approximately,  64,500  webers 
of  useful  flux  passing  through  each  square 
inch  of  armature  section,  at  right  angles  to 
the  course  of  the  magnetic  flux  through  it. 
If,  for  example,  the  armature  core  be  39" 
long,  and  20"  in  effective  width,  the  cross- 
sectional  area  will  be  780  square  inches, 
and  the  probable  amount  of  useful  flux 
carried  by  the  armature  will  be  780  X 
64,500  =  5,030,000  webers. 

The  torque  exerted  by  a  motor  armature 
depends  upon  three  things ;  viz., 

(1)  The  useful  flux  passing  through  the 
armature  in  webers. 

(2)  The      current      strength      passing 
through    the   armature   in   amperes. 

(3)  The  number  of  turns  of  wire ;  i.  e. 
the  number  of  wires  counted  once  around 
the  surface  of  the  armature. 


THE   TRANSMISSION    OF  POWEK.          139 

If  we  multiply  these  three  quantities 
together  and  divide  by  85,155,000,  we 
obtain  the  torque  of  the  motor  in  pounds- 
feet. 

If  the  motor  shown  in  Fig.  21  has  a  cur- 
rent strength  passing  through  its  armature 
by  the  brushes  B,  B,  of  20  amperes,  a  total 
number  of  wires  counted  once  completely 
around  the  surface  of  the  armature, 
amounting  to  160,  and  a  total  flux  passing 
through  the  field  magnets  amounting  to 
5,000,000  webers,  then  the  torque  exerted 
by  the  armature  will  be 

20X160X5,000,000 

85^^00^-   -  187'9  Pounds-feet. 

If  the  pulley  of  this  motor  has  a  radius 
of  one  foot,  then,  neglecting  frictions,  the 
motor  should  be  just  able  to  start  when  a 
weight  of  187.9  pounds  is  suspended  from 
the  periphery  of  its  pulley. 


140  THE   ELECTRIC    MOTOR   AND 

It  will  be  seen,  from  the  foregoing,  that 
the  torque  exerted  by  a  motor  depends 
upon  the  current  strength  passing  through 
its  armature.  If  we  cut  off  the  current 
from  the  armature,  there  will  be  no  torque 
exerted  by  the  motor,  even  though  the 
field  magnets  be  fully  excited  and  their 
maximum  magnetic  flux  produced.  This 
must  evidently  be  the  case,  since  the  cause 
of  the  electro-dynamic  force  is  the  mutual 
interaction  of  the  field  flux  with  the  flux 
produced  by  the  current  through  its  arma- 
ture wires,  and  the  latter  ceases  on  the 
cessation  of  the  current. 

We  may  now  inquire  into  the  causes 
which  determine  the  speed  of  a  motor. 
Let  us  suppose,  for  example,  that  the 
motor  shown  in  Fig.  21,  has  its  field  mag- 
nets excited  from  some  independent  source, 
so  that  the  amount  of  flux  which  passes 


THE  TRANSMISSION   OF  POWER.         141 

through  the  armature  may  be  regarded  as 
constant,  and  equal  to,  say,  5,000,000 
webers.  If  the  armature  be  connected 
through  its  brushes,  B,  B,  with  a  constant 
electric  pressure,  say,  for  example,  with  a 
pair  of  mains  having  a  constant  pressure  of 
10  volts,  then  the  current  strength,  which 
will  tend  to  pass  through  the  armature,  will 
be  controlled  by  Ohm's  law.  Thus,  if  the 

resistance  of  the  armature  were  -r^th    of 

an  ohm,  the  current  strength,  which  would 
tend  to  pass  through  the  armature  at  rest, 

would  be  10  volts  divided  by  —  th    ohm 

=  100  amperes.  If  the  number  of  wires 
upon  the  surface  of  the  armature  be  100, 
counted  once  around,  we  have  seen  that  the 
torque  exerted  by  the  armature,  with  this 
current  strength,  will  be 

100  amperes  X  5,000,000  webers  X  100  wires  _  ,„.  „  ____,,-  fppt 

"-  8' >3  P°unds-feet- 


142  THE  ELECTRIC   MOTOR  AND 

Supposing  the  belt  to  have  been  thrown 
oft*  the  pulley  of  the  motor;  then  under 
this  powerful  torque  the  motor  will  be 
started  in  rapid  rotation.  As  soon  as  the 
armature  commences  to  revolve  through 

o 

the  flux  produced  by  the  field  magnets,  it 
generates  in  the  armature  winding  an  E. 
M.  F.  which  is  counter  or  opposite  to  the 
current  supplied  to  the  armature.  In  other 
words,  the  revolving  motor  armature  com- 
mences to  act  as  a  dynamo  armature,  oppos- 
ing the  current  strength  received  from  the 
mains.  The  effect  of  this  C.  E.  M.  F.  is 
to  reduce  the  amount  of  current  received 
by  the  motor.  If,  for  example,  the  arma- 
ture revolves  at  such  a  rate  as  to  generate 
a  C.  E.  M.  F.  of  5  volts,  the  effective  E.  M. 
F.  acting  in  its  circuit  will  be  10  —  5  =  5 
volts,  and  the  current  will  be  reduced  to  5 

volts  divided  by  TTth  of  an  ohm,  or  to  50 


THE   TRANSMISSION    OF   POWEK.          143 

amperes.  Similarly,  if  the  speed  at  which 
the  armature  runs  is  sufficiently  increased 
to  develop  a  C.  E.  M.  F.  of  9  volts,  the  effect- 
ive E.  M.  F.  in  this  circuit  will  be  10  —  9  = 
1  volt,  and  the  current  will  be  reduced 

to    1     volt    divided    by  -y-th    ohm  =  10 

amperes.  The  armature,  therefore,  accel- 
erates until  such  a  speed  is  reached  as 
will  limit  the  current  passing  through  it  to 
just  the  value  which  is  necessary  in  order 
to  overcome  the  torque  imposed  on  the 
motor ;  i.  e.,  the  resisting  torque. 

The  resisting  torque  will  be  very  small 
if  the  motor  be  disconnected  from  its  belt, 
being  made  up  only  of  the  frictions  of 
bearings,  brushes,  etc.;  while,  if  the  belt 
be  thrown  on  the  motor,  and  it  be  con- 
nected with  a  heavy  load,  the  resisting 
torque  may  be  very  considerable.  The 


144  THE   ELECTRIC   MOTOR   AND 

current  strength  required  to  overcome  this 
torque  is  determined,  as  we  have  seen,  by 
the  flux  through  the  motor,  and  by  the 
number  of  turns  of  wire  lying  upon  its  arm- 
ature. Consequently,  the  speed  of  an  arm- 
ature will  automatically  assume  that  value 
at  which  the  effective  E.  M.  F.;  namely,  the 
difference  between  the  driving  and  C.  E.  M. 
Fs.,  just  enables  this  current  strength  to  be 
supplied  through  the  armature  resistance. 

A  ten  HP  motor,  separately  excited, 
may  be  capable  of  developing  an  E.  M.  F. 
in  its  armature  of  13  volts,  for  every  revolu- 
tion that  it  makes  per  second ;  that  is  to 
say,  if  the  armature  be  set  in  rotation,  in 
any  manner,  at  the  speed  of  one  revolution 
per  second,  or  60  revolutions  per  minute, 
it  \vill  generate  as  a  dynamo  an  E.  M.  F. 
of  13  volts.  If  its  speed  be  altered  to 
3  revolutions  per  second,  its  E.  M.  F. 


THE  TRANSMISSION    OF   POWER.          145 

will  be  39  volts.  If  now  this  motor,  dis- 
connected from  its  load,  be  connected  with 
a  pair  of  mains  having  a  constant  pressure 
between  them  of  208  volts,  the  armature 
will  run  at  a  speed  of,  approximately,  16 
revolutions  per  second,  or  960  revolutions 
per  minute,  and  thereby  generate  an  E.  M. 
F.  counter  or  opposed  to  the  E.  M.  F.  of 
the  mains,  equal  to  16  X  13  =  208  volts; 
for,  the  resisting  torque,  made  up  of  fric- 
tion in  the  armature,  will  be  very  small, 
and  if  the  speed  of  the  motor  falls  below 
16  revolutions  per  second,  or  960  revolu- 
tions per  minute,  the  current  strength, 
which  will  pass  through  the  armature,  will 
be  so  rapidly  increased  that  a  powerful 
electro-dynamic  torque  will  be  exerted 
upon  the  armature  causing  it  to  accelerate, 
and  so  regain  its  full  speed. 

If  there  were  no  friction  whatever  in  the 


146  THE   ELECTRIC   MOTOR   AND 

armature,  which  of  course  is  impossible, 
there  would,  of  course,  be  no  current  and  no 
energy  required  to  drive  the  armature,  and 
if  the  pressure  at  its  terminals  from  the 
mains  were  208  volts,  the  motor  would 
have  to  generate  a  C.  E.  M.  F.  of  ex- 
actly 208  volts,  so  that  by  Ohm's  law  no 
current  would  pass  through  it  and  its 
speed  would  be  steady  at  exactly  16  revo- 
lutions per  second.  If,  however,  a  heavy 
Joad  be  thrown  on  the  motor  producing 
a  powerful  resisting  torque  of,  say  100 
pounds-feet,  then  the  current  strength, 
which  will  be  necessary  to  pass  through 
the  armature  in  order  to  produce  this 
torque,  may  be,  say  20  amperes,  and  if  the 
resistance  of  the  armature  be  1  ohm,  the 
C.  E.  M.  F.  must  drop  to  188  volts  in 
order  that  the  driving  E.  M.  F.  shall  per- 
mit 20  amperes  to  pass  through  this  resist- 
ance;  namely,  208  --  188  =  20  -*-  1  =  20 


PROPERTY  OF 

THE  TRANSMISSION^   POWER.          147 


amperes.     The  speed  on 

loaded  will,  therefore,  drop  to  — -  =  14.46 

1  o 

revolutions   per   second,  or   867.6   revolu- 
tions per  minute. 

Summing  up,  therefore,  if  a  motor  be 
separately  excited,  and  be  connected  with 
a  pair  of  constant-potential  mains ;  i.  e.,  a 
pair  of  mains  maintained  at  an  electrically 
constant  difference  of  pressure  or  voltage, 
the  speed  at  which  it  will  run,  will  de- 
pend upon  the  number  of  wires  lying 
upon  its  armature.  If  the  armature  have 
a  large  number  of  fine  wires,  its  speed  will 
be  comparatively  slow,  since  its  dynamo 
action  and  C.  E.  M.  F.  for  a  given  speed, 
will  be  great ;  or,  in  other  words,  the 
speed  required  to  produce  a  given  C.  E. 
M.  F.  will  be  small.  But  if  the  number 
of  wires  on  the  armature  be  small,  the 


148  THE   ELECTRIC   MOTOR  AND 

speed  at  which  it  will  have  to  run  to 
develop  a  given  C.  E.  M.  F.  will  be  great. 
As  the  torque  imposed  on  the  motor,  or  its 
load  is  increased,  its  speed  will  diminish 
in  order  to  allow  the  necessary  increase  of 
current  to  pass  through  the  motor  to  over- 
come this  torque,  and  the  amount  of  drop 
in  speed  will  depend  upon  the  resistance 
of  the  armature.  If  the  resistance  of  the 
armature  be  comparatively  great,  the  drop 
of  pressure  in  the  armature  will  be  great, 
and  the  speed  must  fall  off  considerably ; 
while,  if  the  resistance  of  the  armature  be 
small,  a  comparatively  small  diminution  in 
speed  will,  by  Ohm's  law,  permit  a  com- 
paratively large  increase  of  current 
strength  and  torque. 

Again,  if  the  pressure  on  the  mains  with 
which  an  armature  is  connected  be  in- 
creased, the  motor  speed  must  increase  in 


THE  TRANSMISSION   OF   POWER.          149 

order  to  develop  a  correspondingly  greater 
C.  E.  M.  F.  Thus,  if  a  motor  runs,  light- 
loaded,  at  a  speed  of  500  revolutions  per 
minute,  when  connected  with  a  pair  of 
110- volt  mains,  it  will  run  with  the  same 
excitation  at,  approximately,  1,000  revolu- 
tions per  minute,  when  connected  with  a 
pair  of  220-Volt  mains.  This  is  evident, 
since,  approximately,  the  same  small  cur- 
rent strength  will  have  passed  through  it 
in  each  case,  and  the  C.  E.  M.  F.  devel- 
oped by  the  motor  armature,  must  be 
'nearly  110  volts  in  the  first  case,  and 
nearly  220  volts  in  the  second. 

We  have  hitherto  assumed  that  the 
amount  of  flux  passing  through  the  ar- 
mature was  constant,  owing  to  separate 
excitation  of  the  field  magnets.  It  is  evi- 
dent, however,  that  if  the  flux  passing 
through  the  armature  be  varied,  the  speed 


150  THE   ELECTRIC    MOTOR   AND 

will  also  vary.  Thus,  if  the  machine 
already  considered,  which  had  a  flux  of 
5,000,000  webers,  and  100  wires  on  its 
armature,  when  connected  with  a  pressure 
of  10  volts,  made  a  speed  of  10  revolu- 
tions per  second,  or  600  revolutions  per 
minute ;  then,  if  we  reduce  the  flux  passing 
through  the  armature  by  one  half,  or  to 
2,500,000  webers,  the  speed  will  be  practi- 
cally doubled,  or  increased  to  20  revolu- 
tions per  second,  or  1,200  revolutions  per 
minute.  This  is  for  the  reason  that  the 
armature  must  run  faster  through  the 
weaker  flux  in  order  to  generate  a  given 
C.  E.  M.  F.  If  one  revolution  per 
second  produced  one  volt  in  a  stronger 
flux,  two  revolutions  per  second  would  be 
required,  per  volt,  in  the  weaker  flux. 
Consequently,  we  may  always  increase  the 
speed  of  a  motor  by  weakening  its  field 
flux ;  i.  e.j  by  diminishing  the  current 


THE   TRANSMISSION    OF   POWER.          151 

strength  circulating  in  the  field  coils,  and 
their  M.  M.  F.  There  will,  of  course,  be 
a  limit  to  the  degree  at  which  this  acceler- 
ation can  be  produced,  since,  if  the  flux  is 
very  much  weakened,  the  flux  produced 
by  the  current  in  the  armature  winding 
will  overpower  that  of  the  field,  and  may 
actually  reverse  it,  thus  tending  to  destroy 
the  C.  E.  M.  F.  of  the  armature,  diminish- 
ing its  torque  indefinitely,  and  requiring  an 
indefinitely  high  speed  to  check  the  cur- 
rent strength,  and  the  machine  will  there- 
fore stop.  On  the  other  hand,  if  we 
increase  the  current  strength  passing 
through  the  field  magnet  coils,  and  so 
increase  their  M.  M.  F.,  they  will  develop 
a  greater  magnetic  current  or  flux  in  the 
magnetic  circuit  of  the  machine,  including 
the  armature,  and  this  increased  flux  will 
produce  the  C.  E.  M.  F.  required  from  the 
motor  at  a  correspondingly  reduced  speed. 


152 


THE   ELECTRIC    MOTOR   AND 


In  practice,  motors  are  not  usually  sepa- 
rately excited,  but  are  excited  by  a  cur- 
rent obtained  from  the  mains  supplying 
the  armature.  The  field  winding  may  be 
connected  either  in  series  with  the  arma- 
ture, producing  what  is  called  a  series- 


FIG.  26. — DIAGRAM  OF  SHUNT  WINDING. 

wound  motor,  or  in  shunt  with  the 
armature,  producing  what  is  called  a 
shunt-wound  motor.  Fig.  26,  represents  dia- 
grammatically  the  connections  of  a  shunt- 
wound  motor.  Here  the  ends  b  and  c,  of 
the  magnetic  coils  M,  are  connected  in 
shunt  with  the  ends  d  and  0  of  the  ar- 


THE  TRANSMISSION    OF   POWER.          153 

mature  A.  a  and  f,  are  the  constant- 
potential  mains.  If  the  resistance  of  the 
magnet  M,  be  assumed  constant,  by  Ohm's 
law  the  current  strength  through  it 
must  be  constant,  and  the  effect  is  the 
same  as  though  the  motor  were  separately 
excited.  The  strength  of  current,  which 
the  armature  can  carry  continuously,  de- 
pends upon  its  size,  winding  and  construc- 
tion. The  drop  of  pressure,  which  its 
full-load  current  will  produce,  usually 
varies  between  2  per  cent,  and  10  per 
cent,  of  the  terminal  pressure ;  that  is  to 
say,  if  the  pressure  between  the  mains  a 
and/,  be  500  volts,  then  the  full-load  drop 
in  the  armature  will  usually  vary  between 
50  volts  in  a  small  motor,  and  10  volts  in 
a  large  motor,  the  C.  E.  M.  F.  at  full 
load  being  respectively  450  and  490  volts. 
The  drop  in  speed  of  such  a  motor  will, 
therefore,  usually  vary  between  10  per 


154 


THE   ELECTRIC    MOTOR   AND 


cent,  and  2  per  cent.,  according  to  the  size 
of  the  machine,  and,  within  these  limits,  the 
machine  automatically  regulates  its  speed 
according  to  the  load. 

The  connections  of  a  series-wound  motor 
are  shown  in   Fig.  27.     Here  the  magnet 


FIG.  27. — DIAGRAM  OF  SERIES  WINDING. 

coil  M,  is  in  series  with  the  armature  A, 
between  the  mains  a  and/;  that  is  to  say 
the  current  from  the  mains  passes  succes- 
sively through  the  magnet  M,  and  arma- 
ture A.  When  such  a  machine  is  on  light 
load,  with  a  small  torque,  the  current 


&J!Bc'WRTY  CF 


THE   TRANSMISSION 

strength  passing  through  tB 
be  comparatively  small,  and 
of  this  current  in  the  field  coils  will  T)e 
small,  producing  thereby  a  small  magnetic 
flux  through  the  armature.  The  speed  of 
the  armature  will,  therefore,  be  compara- 
tively great.  If,  however,  the  torque  on 
the  motor ;  i.  'e.,  its  load,  be  increased,  the 
current  passing  through  the  motor  will 
automatically  increase,  increasing  thereby 
the  M.  M.  F.  and  flux  through  the 
armature,  thus  reducing  the  speed.  On 
this  account,  as  well  as  owing  to  the  drop 
of  pressure  in  the  resistance  of  the  arma- 
ture, a  series-wound  motor  is  much  more 
variable  in  its  speed  than  is  a  shunt- wound 
motor,  but  a  series-wound  motor,  espe- 
cially in  small  sizes,  is  simpler  to  construct ; 
for,  its  field- winding  consists  of  but  com- 
paratively few  turns  of  coarse  wire,  while 
a  shunt  motor  field-winding  consists  of 


156 


THE   ELECTRIC   MOTOR   AND 


many  turns  of  fine  wire,  in  order  to  reduce 
as  far  as  possible  the  current  strength 
employed  in  magnetizing  them. 

A   compound-wound  motor  is   a   motor 
whose  field     magnets    are     partly    series- 


FIG.  28.— DIAGRAM  OF  COMPOUND  WINDING. 

wound  and  partly  shunt- wound.  Such  a 
winding  is  diagrammatically  represented  in 
Fig.  28.  Here  the  armature  A,  is  in  series 
with  the  coarse  wire  coils  m,  and  these  two 
are  connected  in  shunt  with  the  fine  wire 
coil  .Af.  When  no  current  passes  through 
the  armature,  the  field  magnet  M,  is  excited, 


THE  TRANSMISSION   OF   POWER.          157 

while  the  series  coil  m,  is  un magnetized. 
When  the  full-load  current  passes  through 
the  armature,  the  excitation  of  the  series  coil 
m,  reaches  its  maximum.  The  M.  M.  F. 
of  ra,  is  counter  or  opposed  to  the  M.  M.  F. 
of  J/J  so  that  the  magnetic  flux  is  slightly 
weakened  at  full  load,  thereby  necessitat- 
ing a  slight  acceleration  of  the  armature  in 
order  to  develop  its  C.  E.  M.  F.  This  ac- 
celeration may  be  adjusted  so  as  to  almost 
completely  counterbalance  the  drop  in 
speed,  which  would  otherwise  take  place 
by  virtue  of  the  drop  of  pressure  in  the  re- 
sistance of  the  armature,  considered  as  a 
separately-excited  machine.  A  compound - 
wound  motor  may,  therefore,  be  adjusted 
so  as  to  have  a  practically  constant  speed 
under  all  loads. 

Tlie  activity  absorbed  by  a  motor  is  usu- 
ally measured  as  the  product  of  the  termi- 


158  THE   ELECTRIC   MOTOR   AND 

nal  pressure  in  volts  and  the  current 
strength  in  amperes.  Thus,  if  the  motor 
be  connected  with  a  pair  of  220-volt  mains, 
and  be  observed  to  take  a  total  current  of 
10  amperes,  then  the  activity  absorbed  by 
the  motor  will  be  220  volts  X  10  amperes  = 
2,200  watts  =  1,622  foot-pounds-per-second 
=  2.2  kilowatts  =  2.949  horse-power.  If 
the  motor  were  a  perfect  machine,  expend- 
ing no  internal  activity,  under  these  condi- 
tions, it  would  do  mechanical  work  at  a 
rate  of  2,200  watts,  or  1,622  foot-pounds- 
per-second,  but  its  actual  efficiency  would, 
probably,  be  about  82  per  cent,  in  this  size. 

of  machine,  and  the  mechanical  activity  it 

09 
would  exert,  would  be  2,200  X         =  1,804 


watts  =  1,330  foot-pounds-per-second.  The 
motor  could,  therefore,  lift  1  pound  1,330 
feet  per  second,  or  133  pounds  10  feet  per 
second,  at  this  load. 


THE   TRANSMISSION   OF   POWER.          159 

The  efficiency  of  motors  varies  with 
their  size.  A  very  small  motor,  such  as 
that  employed  for  driving  a  desk  fan,  has 
an  efficiency  of,  probably,  only  30  per  cent., 
while  a  1  horse-power  motor  will,  prob- 
ably, have  an  efficiency  of  60  per  cent.,  and 
a  100  horse-power  motor  an  efficiency  of, 
probably,  90  per  cent.  The  efficiency  may 
be  even  still  greater  in  larger  sizes,  al- 
though, of  course,  it  can  never  reach  100 
per  cent.,  since  some  activity  is  sure  to  be 
lost  within  the  motor. 

It  should  be  clearly  borne  in  mind  that 
all  improvements,  which  have  yet  to  be 
made  in  electro-dynamic  motors,  must  be 
almost  entirely  confined  to  the  directions  of 
reduced  speed  or  reduced  cost,  because  the 
efficiency  is  already  so  comparatively  high. 
If  a  100  horse-power  motor  only  wastes 
about  10  horse-power  at  full  load,  in  its 


160  THE  ELECTRIC   MOTOR  AND 

mechanical  and  electrical  frictions,  the 
best  possible  motor  of  this  size  could  only 
save  10  horse-power  under  the  same  condi- 
tions. The  direction,  in  which  we  may 
look  forward  to  improvements  in  motors, 
lies,  therefore,  almost  wholly  in  reducing 
their  cost  of  construction  and  the  speed  at 
which  they  run. 

The  work  absorbed  by  an  electric 
motor  from  the  circuit  supplying  it  is 
conveniently  measured  in  units  called 
Idlowatt-liours,  a  kilowatt-hour  being  an 
amount  of  work  equal  to  that  performed 
by  an  activity  of  one  kilowatt  maintained 
steadily  for  one  hour.  A  kilowatt-hour  is 
equal  to  1.34  (roughly  1  1/3)  horse -power- 
hours,  or  to  3,600,000  joules,  or  2,663,000 
foot-pounds.  In  Great  Britain  the  kilo- 
watt-hour is  called  the  "  Board  of  Trade 
Unit." 


THE  TRANSMISSION   OF   POWER.          161 

The  work  consumed  by  an  electric 
motor  is  usually  measured  by  a  meter  placed 
in  its  circuit.  The  meter  may  be  a  watt- 
meter, in  which  case  its  dial  will  show  the 
total  amount  of  work  received  by  the 
motor  in  kilowatt-hours;  or  it  may  be 
an  ampere-hour  meter,  whose  indications, 
multiplied  by  the  pressure  of  the  circuit, 
assumed  as  uniform,  will  give  the  total 
amount  of  work  consumed.  Thus,  if  a 
motor  connected  with  a  220-volt,  constant- 
potential  circuit,  is  shown  to  have  received 
5,000  ampere-hours  in  a  month,  by  the 
record  of  an  amperediour  meter,  the  total 
work  it  has  received  will  be  5,000  X  220 
=  1,100,000  watt-hours  =  1,100  kilowatt- 
hours. 


CHAPTER  VI. 

STRUCTURE    AND    CLASSIFICATION    OF    MOTORS. 

TURNING  uow  to  the  practical  construc- 
tion of  motors,  let  us  look  at  the  motor 
shown  in  Fig.  29,  and  in  order  to  under- 
stand its  construction,  let  us  take  it  apart 
and  study  it  in  detail  as  shown  in  Fig.  30. 
In  these  figures,  corresponding  numerals 
represent  corresponding  parts.  1,  is  the 
completed  armature,  mounted  on  its  shaft, 
with  a  commutator  at  one  end,  and  with 
the  insulated  winding  wrapped  round  and 
round  the  iron  core  or  body,  and  suitably 
connected  with  the  commutator.  The 
shaft  rests  in  journals  15  and  18,  sup- 
ported on  pedestals  13  and  16.  These 


162 


THE   TRANSMISSION   OF   POWER. 


163 


bearings  are  self  -oiling  ;  that  is  to  say,  they 
contain  oil  which  is  continually  poured 
upon  the  surface  of  the  revolving  shaft  by 


17 


FIG.  29. — FORM  OP  ELECTRIC  MOTOR. 

the  action  of  the  rings  19,  as  will  be  later 
explained. 

On  the  end  of  the  shaft  opposite  to  the 
commutator  is  secured  the  pulley  5.     The 


164  THE    ELECTRIC   MOTOR. 

pedestals  themselves  rest  upon  the  cast- 
iron  base  plate  8,  to  which  they  are  firmly 
secured  by  bolts.  This  base  plate  forms 
part  of  the  magnetic  circuit  of  the  machine. 
Upon  its  smooth  surface  are  bolted  the 
field  cores,  3,  3,  on  the  heads  of  which 
stand  the  pole  pieces  2,  2.  The  pole 
pieces  are  set  in  place  after  the  magnets 
coils  4,  4,  are  set  in  position.  The 
rocker  arm  21,  carries  the  two  brush 
holders  22,  22,  in  insulated  sockets  at  each 
extremity,  and  the  brush  holders,  in  their 
turn,  clamp  the  metallic  brushes  23,  23, 
which  rest  upon  the  surface  of  the  com- 
mutator at  diametrically  opposite  points. 
By  moving  the  handle  of  the  rocker  arm, 
the  diameter  upon  which  the  brushes  bear 
on  the  commutator,  called  the  diameter  of 
commutation,  can  be  varied  within  suitable 
limits;  24,  are  the  cables  connecting  the 
brushes  with  the  terminals  6  and  7,  mounted 


I   PROPERTY  Cf 


166 


THE   ELECTRIC   MOTOR. 


on  a  board  above  the  pole-pieces,  and  to 
which  the  main  leading  wires  are  attached. 
The  rods  12,  12,  securely  bolt  the  cores 


FIG.  31. — FORM  OP  CONTINUOUS-CURRENT  MOTOR. 

and  pole-pieces  to  the  base  plate,  and  also 
leave  eye-bolts  by  which  the  machine  can 
be  readily  slung. 


168  THE   ELECTRIC    MOTOR   AND 

The  motor  shown  in  Fig.  31,  differs 
from  that  in  Fig.  29,  in  the  fact  that  the 
armature  and  pole-pieces  are  supported 
close  to  the  base,  so  that  the  field  magnets 
are  inverted.  In  other  respects,  however, 
the  parts  are  similar  in  each  motor.  This 
motor  is  shown  dissected  in  Fig.  32,  where, 
as  before,  corresponding  parts  are  marked 
with  corresponding  numerals.  It  is  im- 
portant to  notice  that  in  order  to  prevent 
the  magnetic  flux  produced  by  the 
M.  M.  F.  of  the  coils  12,  from  passing 
entirely  through  the  cast  iron  base,  the 
pole-pieces  are  supported  on  slabs  of 
zinc  5,  which  introduces  a  greater  reluc- 
tance into  this  path  and  enables  almost  all 
of  the  magnetic  flux  to  pass  through  'the 
armature  core. 

In  order  to  obtain  a  better  conception 
of  the  construction,  we  may  now  consider 


THE   TRANSMISSION    OF   POWER. 


169 


FIG.  33. — MOTOR  WITH  RING  ARMATURE. 

the  separate  parts  of  the  motor  in  fur- 
ther detail,  beginning  with  the  armature. 
Broadly  speaking,  armatures  may  be 
divided  into  three  classes;  namely, 

(1)  Drum  armatures. 

(2)  Ring  armatures. 

(3)  Disc  armatures. 


170  THE   ELECTRIC    MOTOR   AND 

Figs.  22,  29,  30,  31,  and  32  represent 
drum  armatures;  that  is  to  say,  armatures 
which  are  simply  drum-shaped  or  cylin- 
drical in  their  appearance. 


FIG.  34. — MOTOR  WITH  GRAMME  RING  ARMATURE. 

Fig.  33,  represents  a  motor  furnished 
with  a  ring  armature  A  A  A.  Here  the 
field  magnets  are  placed  inside  the  arma- 
ture, as  is  sometimes  the  case,  though 
more  frequently  the  armature  is  placed 
inside  the  field,  as  is  shown  in  Fig.  34, 


THE   TRANSMISSION   OF   POWER.          171 


FIG.  35.— Disc  ARMATURE. 


172  THE   EL  EOT  HIC    MOTOR   AND 

where  the  armature  A,  is  placed  between 
the  poles  N  and  8,  of  the  magnet  M. 

An  example  of  a  disc  armature  is  shown 
in  Fig:.  35.     Here  a  number  of  insulated 

O 

radial  conductors  C,  C,  are  held  like  spokes 
in  a  wheel,  and  are  connected  together 
by  conducting  strips  #,  $,  s,  at  the  centre 
and  edge  of  the  wheel.  In  this  arma- 
ture the  conducting  bars  &,  &,  &,  on  the 
periphery  of  the  wheel,  form  the  commu- 
tator upon  which  the  collecting  brushes 
are  intended  to  rest.  Fig.  36  represents 
the  complete  machine  employing  this 
armature.  The  magnets  are  here  enclosed^ 
in  a  field  frame,  and  present  their  polar 
surfaces  to  each  other  across  the  disc 
armature.  Disc  armatures  are  very  seldom 
used  in  the  United  States. 

A  drum  or  ring  armature  consists  esseri- 
tially-of  three  parts ;  namely, 


THE   TRANSMISSION 


FIG.  36.  —  Disc  ARMATURE  MOTOR. 


(1)  The  00r0  or  body,  which  is  always  of 
soft  iron. 

(2)  The  exciting  coils,  of  insulated  cop- 
per wire,  which  are  wound  upon  the  core, 
and  in  which  the  E.  M.  F.  is  generated  by 
revolution  through  the  flux. 

(3)  The     commutator,    by     means     of 


174  THE   ELECTRIC    MOTOR   AND 

which  the  E.  M.  F.'s  induced  in  the  coils 
are  united  and  co-directed  so  as  to  pro- 
duce a  continuous  E..M.  F.  in  the  circuit ; 
or,  regarded  from  a  different  standpoint, 
the  commutator  distributes  the  cur- 
rent received  from  the  external  circuit 
through  the  armature  winding,  in  such  a 
manner  as  to  produce  a  continuously  act- 
ing torque; 

Armature  cores  may  be  divided,  from 
another  standpoint  into  two  classes ;  viz., 
the  smooth-core  and  the  toothed-core. 
Smooth-core  armatures  present  a  continu- 
ously smooth,  cylindrical  surface  before  the 
wire  is  wound  upon  them.  Such  a  core  is 
shown  in  Fig.  37.  Here  /?,  8,  is  a  steel 
shaft,  which  carries  two  phosphor-bronze 
spiders,  one  of  which  only  is  seen  at  B. 
These  spiders  are  clamped  to  the  shaft  and 
support  between  them  the  hollow  core 


THE  TRANSMISSION   OF  POWER. 


175 


(7,  <7,  which  consists  of  a  number  of  thin, 
soft  iron  plates,  or  annular  discs,  which 
after  being  assembled,  are  pressed  together 


FIG.  37.— SMOOTH-CORE  ARMATURE  BODY. 

and  then  clamped  by  a  spider  between  the 
end  plates  P. 

In  the  early  history  of  the  art,  armature 
cores  were  constructed  of  solid  masses  of 
soft  iron ;  but  it  was  soon  found  that  such 
cores  became  intensely  heated  when  re- 


176  THE   ELECTRIC   MOTOR   AND 

volved  through  the  field  flux,  even  though 
no  insulated  wire  was  wound  upon  their 
surfaces.  This  heating  was  owing  to  the 
fact  that  E.  M.  F.'s  were  induced  in  the 
conducting  iron  mass,  which  set  up  pow- 
erful electric  currents,  called  eddy  currents, 
through  its  substance.  These  eddy  cur- 
rents did  no  useful  work,  and  expended 
power  prejudicially  in  heating  the  core. 
By  using  laminated  cores  j  i.  e.,  by  divid- 
ing the  core  into  a  number  of  separate 
discs,  with  their  planes  at  right  angles  to  its 
axis,  while  the  passage  of  the  magnetic  flux 
is  not  impeded,  since  it  passes  directly 
through  each  disc,  in  its  own  plane,  the  eddy 
currents,  which  tend  to  develop  in  a  direc- 
tion at  right  angles  to  the  plane  of  the 
discs,  are  very  greatly  checked  and  impeded 
on  account  of  the  resistance  offered  to  their 
passage  through  the  pile  of  discs.  Conse- 
quently, the  loss  of  power  from  eddy  cur- 


THE  TRANSMISSION   OF   POWER. 


177 


rents  is  very  greatly  reduced  by  this 
expedient  of  laminating  the  core,  or  build- 
ing it  of  separate  discs,  and  the  process  is 
invariably  adopted  except  in  the  very 
smallest  motors. 


FIG.  38.— TOOTHED-CORE  ARMATURE  IN  VARIOUS  STAGES 
OP  CONSTRUCTION. 

Toothed-core  armatures  are  those  which 
possess  corrugated  surfaces,  like  a  cog 
wheel.  Such  a  toothed-core  armature  is 
shown  in  Fig.  38  at  A.  It  will  be 
observed  that  the  surface  of  this  core  is 
indented  with  grooves,  running  parallel  to 


178  THE   ELECTRIC    MOTOR   AND 

the  axis  of  the  shaft.  In  these  grooves 
the  conducting  wires,  protected  by  suit- 
able insulating  material,  are  subsequently 
laid.  At  J3,  the  armature  is  shown  with 


FIG.  39. — ASSEMBLAGE  OP  LAMINATED  ARMATUKE  CORE 
Discs. 

its  winding  in  place,  following  the  grooves. 
At  6Y  the  complete  and  covered  armature 
is  shown.  Fig.  39,  shows  a  method  of 
assembling  toothed-core  armatures  upon  a 
shaft,  so  as  to  form,  when  completed,  a 


THE   TRANSMISSION    OF   POWER.          179 

drum  armature.  Here  Ay,  >SJ  is  the  shaft, 
6',  the  assembled  discs,  and  r,  <•,  the  discs 
ready  to  be  assembled. 

It  will  be  observed  that  when  com- 
pleted, and  wound  with  wire,  both  the 
toothed-core  and  the  smooth-core  arma- 
tures are  alike,  in  that  they  both  present 


FIG.  40.— COMPLETED  SMOOTH-CORE  ARMATURE. 

a  continuous  cylindrical  surface,  but  in  the 
smooth-core  armature  this  surface  is 
formed  entirely  of  insulated  wire  wrhich 
completely  covers  and  hides  the  iron  core. 
In  the  toothed-core  armature,  however,  the 
iron  teeth  or  projections  extend  to  the  sur- 
face, and  remain  uncovered  by  wire,  which 
only  fills  the  grooves  between  adjacent 


180  THE   ELECTRIC    MOTOR   AND 

teeth.  Tli us  Fig.  40,  shows  a  completed 
smooth-core,  drum-armature,  with  the  in- 
sulated conducting  wire  lying  over  its  sur- 
face, parallel  to  the  axis.  In  this  arma- 
ture it  is  necessary  to  hold  the  wire 
securely  in  place  by  binding  the  brass 


FIG.  41. — COMPLETED  TOOTHED-CORE  ARMATURE. 


wire  b,  />,  />,  tightly  over  mica  strips  and 
soldering  it  in  position.  The  ends  of  the 
armature  are  covered  -  by  canvas  supported 
on  circular  heads  A,  k. 

Fig.    41,    shows   a   completed    toothed- 
core  drum   armature.     Here,    as    will     be 


THE  TRANSMISSION   OF   POWER.  181 

seen,  the  external  surface  of  the  armature 
consists  of  iron,  between  the  bands  b,  1). 

Fig.  42  represents  a  portion  of  one  of 
the  discs  of  a  toothed-core  armature.     The 


FIG.  42. — PORTION    OP   Disc    OF  LAMINATED  TOOTHED- 
CORE  ARMATURE. 


circular  holes  are  for  the  clamping  bolts, 
while  the  grooves  are  intended  for  the 
reception  of  the  insulated  wires. 

It  will  thus  be  seen  that  a  toothed-core 
armature  is  much  more  solid  and  secure, 
when  completed,  than  the  smooth-core 


182  THE   ELECTRIC    MOTOR. 

armature,  arid,  partly  for  this  reason,  the 
toothed-core  .aiunatures  have  come  into 
general,  use.  It  is  evident  that  the 
toothed-core  armature  does  not  require 
bauds  on  its  surface  to  keep  the  wires  in 
place.  Moreover,  the  length  of  the  air- 
gap  or  entrefer ;  that  is  to  say,  the  dis 
tance  between  the  iron  in  the  armature 
and  the  polar  faces  of  the  field  magnets,  is 
greatly  reduced,  thereby  reducing  the 
reluctance  of  the  magnetic  circuit,  and  re- 
quiring much  less  M.  M.  F.  in  the  field 
magnet  coils  to  produce  a  given  amount  of 
flux  through  the  armature. 

Fig.  43  represents  the  winding  of  a 
toothed-core  armature  B.  Here,  as  will 
be  seen,  the  cotton  covered  wires  are 
passed  through  the  grooves.  A,  shows  a 
complete  armature  with  the  wire  con- 
nected to  the  commutator  (7. 


PROFE    FYCF 


184  THE   ELECTRIC    MOTOR   AND 

A  simple  form  of  commutator,  called  a 
two-part  commutator  is  shown  in  Fig.  44. 
Such  a  commutator  would  be  suitable  for 
commuting  the  current  produced  in  a  single 
loop  of  wire  on  an  armature  rotated  in  a 


FIG.  44. — DIAGRAM  OP  TWO-PART  COMMUTATOR. 

bipolar  field.     In  this  commutator  the  wire 

W2,  is  connected  to  the  segment   6'2,  and 

the  wire  W1,  to  the  segment  6Y1.     Under 

these  conditions,  if  the  E.  M.  F.  generated 

in  the  loop  whose  terminals  are    W1  and 

W2,  be  in  such  a   direction  that    W1,  is 


THE   TRANSMISSION    OF   POWER.          185 

positive  and  W2,  negative,  the  current  will 
flow  from  W1,  to  (71,  and  out  from  the 
brush  JS\  through  the  external  circuit 
connecting  the  brushes,  and  return  through 
the  brush  7?2,  the  segment  <72,  and  the 
wire  W2.  After  a  quarter  of  a  revolution 
has  bsen  effected  from  the  position  shown, 
and  in  the  direction  indicated  by  the 
arrows,  the  brush  .Z?1,  will  rest  on  the  seg- 
ment C2y  and  the  brush  B2,  on  the  seg- 
ment (71.  At  the  same  moment,  however, 
if  the  commutator  is  properly  placed,  the 
E.  M.  F.  which  is  being  generated  in  the 
loop  will  be  reversed  by  its  passage  before 
the  magnet  poles.  TP2,  will  therefore  be 
the  positive  pole  under  the  new  conditions. 
The  current  will  consequently  flow  from 
W2,  to  C2,  and  brush  J3\  and  return  after 
traversing  the  external  circuit  through 
jE>2,  segment  6n,  and  wire  Wl.  Conse- 
quently, although  the  E.  M.  F.  in  the 


186  THE   ELECTRIC    MOTOR   AND 

armature  has  been  reversed,  the  brush 
J3lj  is  still  positive,  and  the  current  in 
the  external  circuit  preserves  its  direction. 
No  matter  how  many  bars  a  commutator 
may  possess,  and  no  matter  how  many 
wires  or  loops  are  undergoing  cornmuta- 

v  v 


b1 

FIG.  45 — ARRANGEMENT  OP  BRUSHES  ON  A  COMMUTATOR. 

tion,  the  effect  will  be  essentially  the  same 
as  that  here  described. 

The  arrangement  of  brushes  resting  in 
contact  with  a  commutator,  for  such  a  motor 
as  is  shown  in  Fig.  31,  is  represented  in 
Fig.  45.  Here  b,  b,  I1,  bl,  are  two  pairs  of 
brushes,  each  pair  being  connected  electric- 


THE   TRANSMISSION   OF   POWER.  187 

ally  together  and  resting  upon  the  commu- 
tator bars.  The  brushes  consist  of  metallic 
strips  or  bundles  of  wire,  usually  of  copper, 
but  sometimes  consisting  of  carbon  blocks. 
They  are  held  in  place  by  devices  called 
brush-holders,  a  form  of  which  is  shown  in 
Fig.  46.  Springs  placed  in  these  brush- 


FIG.  46.— BnusH-HoLDERS. 

holders  maintain  a  uniform  electric  pressure 
between  the  brush  and  the  commutator. 
After  the  brushes  have  been  so  set  as  to 
press  upon  opposite  segments  of  the  com- 
mutator, they  can  be  rotated  together  into 
any  suitable  position  by  the  rocker  arm, 


188  THE   ELECTRIC   MOTOR  AND 

which  is  represented  at  21,  in  Fig.  30,  and 
at  44,  in  Fig.  32. 

We  have  seen  that  in  all  motors  a  certain 
amount  of  energy  is  uselessly  expended  in 
the  friction  between  the  revolving  shaft 
and  its  supports.  In  order  to  lessen  this 
as  much  as  possible  the  bearings  are  kept 
well  lubricated.  In  practice  this  is  almost 
invariably  secured  by  means  of  automatic 
oilers,  that  is,  by  bearings  which  automa- 
tically keep  the  rubbing  surfaces  lubri- 
cated. Such  an  automatic,  self -oiling 
bearing  is  shown  in  Fig.  47.  Here  the 
shaft  is  supported  in  the  sleeve  8,  of  a 
special  alloy,  called  Babbitt  metal,  having 
grooves  cut  in  its  interior,  so  as  to  dis- 
tribute the  oil  freely  over  the  revolving 
surface  of  the  shaft  by  the  action  of  rota- 
tion. This  action  is  facilitated  by  the 
action  of  two  rings  H,  R,  which  rest 


THE   TRANSMISSION   OF   POWER. 


189 


upon  the  shaft  in  grooves  cut  into  the 
Babbitt  metal  sleeve.  These  rings  dip 
beneath  the  surface  of  the  oil  in  the 


FIG.  47. — AUTOMATIC  SELF-OILING  BEARING. 

reservoir  O.  As  the  shaft  revolves  it  sets 
the  ring  into  rotation,  although  the  rota- 
tion may  be  many  times  less  rapid  than 


190 


THE   ELECTRIC   MOTOR   AND 


that  of  the  shaft.  The  rings  cany  oil  on 
their  surfaces  up  into  the  grooves  and  dis- 
tribute this  over  the  shaft.  The  oil,  after 
passing  through  the  bearing,  drips  again 
into  the  reservoir  O.  The  level  of  the  oil 
in  the  reservoir  can  be  observed  by  means 
of  the  gauge  glass  G.  The  sleeve  /SJ  and 


FIG.  48. — DETAILS  OF  SELF-OILING  BEARING. 

its  brass  rings,  are  shown  in  greater  detail 
in  Fig.  48. 

The  field  magnets,  the  function  of  which 
is  to  produce  the  flux  passing  through  the 
armature,  consist  essentially  of  coils  of  in- 
sulated wire,  provided  with  cores  and  pole 


THE   TRANSMISSION    OF   POWER. 


191 


pieces,  shaped  so  as  to  produce  an  annular 
or  cylindrical  space  for  the  rotation  of  the 
armature.  In  Fig.  30,  the  field  magnet 
cores,  with  their  pole  pieces,  are  shown 


FIG.  49. — SKELETON  OF  MOTOR  PARTS. 

at  3  and  2,  respectively.  The  coils  of 
insulated  wire  which  surround  them  are  in 
practice  wound  on  spools  so  that  the  entire 
coil  can  be  readily  removed  from  the  core. 
Such  a  coil  is  shown  at  4,  in  Fig.  30.  The 


192 


THE   ELECTRIC   MOTOR   AND 


cast-iron  base  of  the  machine  forms  part  of 
the  magnetic  circuit,  as  already  mentioned. 


FIG.  50.— COMPLETE  MOTOR  OF  TYPE  SHOWN  IN  FIG.  49. 

In  Fig.  49,  a  skeleton  representation  of 
the  different  parts  of  a  particular  form  of 
motor,  is  shown  in  place.  Here  the  arma- 
ture, with  its  commutator  and  pulley,  is 
mounted  between  the  pole  pieces  of  the 
electromagnet  as  shown.  In  this  machine, 


THE   TRANSMISSION   OF   POWER.          193 

•> 

the  field  cores  (7,  C,  are  clamped  by  bolts 
in  recesses  prepared  for  their  reception  in 
the  cast-iron  bed  plate.  A  complete  ma- 
chine of  the  same  type  is  shown  in  per- 
spective in  Fig.  50. 

Since  the  torque  of  a  motor  depends 
upon  the  amount  of  flux  passing  through 
the  armature,  upon  the  current  strength  it 
carries,  and  upon  the  number  of  wires 
lying  on  the  surface  of  the  armature,  it  is 
evident  that  a  powerful  torque  necessitates 
a  powerful  flux,  a  powerful  current,  and  a 
great  number  of  wires.  As  we  increase 
these,  we  must  increase  the  size  of  the 
machine.  Consequently,  powerful  motors, 
are  necessarily  large,  heavy  motors. 

It  may  be  interesting  to  note  the  weight 
and  dimensions  generally  given  to  motors  of 
various  sizes.  A  half-horse-power  motor 
of  good  type,  weighs  about  100  pounds, 


194  THE   ELECTRIC    MOTOR   AND 

or  about  200  pounds  per  horse-power,  and 
occupies  a  floor  space  of  18"  x  10."  A 
5-borse-power  motor,  of  good  type,  weighs 
about  600  pounds,  or  120  pounds  per 
horse-power,  and  occupies  a  floor  space  of 
28"  x  20".  A  15-horse-power  motor  of 
good  type,  weighs  about  1,500  pounds,  or 
100  pounds  per  horse-power,  and  occupies 
a  floor  space  of  4'  6"  x  3'.  A  60-horse- 
power  motor  weighs  about  6,000  pounds, 
or  about  100  pounds  per  horse-power,  and 
occupies  a  floor  space  of  about  7'  x  5', 
while  a  250-horse-power  motor  would  have 
a  weight  of  about  25,000  pounds,  or  100 
pounds  per  horse-power,  and  a  floor  space 
of  11'  x  6'.  It  will  be  seen,  therefore, 
that  small  motors  weigh  about  200 
pounds  per  horse-power — or  746  watts 
(roughly  750  watts) — of  full-load  me- 
chanical output,  and  large  motors  about 
100  pounds  per  horse-power.  The  slower 


THE  TRANSMISSION   OF   POWER.          195 

the  speed  at  which  a  motor  is  designed  to 
run,  the  greater  will  be  its  weight,  other 
things  being  equal. 

It  is  convenient  to  remember  that  for 
motors  up  to  10-horse-power,  the  number 
of  horse-power  delivered  is  roughly  equal 
to  the  number  of  kilowatts  absorbed  at 
the  motor  terminals.  For  example,  a  6- 
horse-power  motor,  delivering,  therefore, 
4,476  watts  mechanically,  absorbs  roughly 
6  kilowatts,  or  6,000  watts,  at  its  terminals, 
whether  the  machine  be  built  for  circuits 
of  100  volts,  200  volts  or  500  volts.  This 
rule  presupposes  a  commercial  efficiency  of 
74.6  per  cent.  In  large  sizes  the  efficiency 
increases  and  the  rule  cannot,  therefore, 
be  relied  upon.  Thus  a  machine  which 
has  a  full-load  output  of  120  horse-power, 
or  about  90  KW,  has  an  intake  of,  approxi- 
mately, 100  KW. 


196  THE   ELECTRIC   MOTOR  AND 

The  speed  of  motors  depends  upon  their 
size  and  construction.  If  two  motors  have 
the  same  weight,  floor  space,  efficiency,  and 
cost,  the  one  which  has  the  slower  speed 
of  revolution  is  the  better  machine  of  the 
two,  because,  by  rewinding  it  for  the 
higher  speed  it  could  be  made  to  have  a 
greater  output,  that  is  to  be  the  equiva- 
lent of  a  heavier  machine.  The  speed  of 
a  1/2-horse-power  motor  of  good  type  is 
about  1,300  revolutions  per  minute  at  full- 
load  ;  that  of  a  1-horse-power  motor,  about 
1,000  revolutions  per  minute ;  of  a  5- 
horse-power  motor,  900  revolutions  per 
minute;  a  15-horse-power  motor,  750  revo- 
lutions ;  a  120-horse-power  motor,  about 
550  revolutions  and  a  250-horse-power 
motor,  about  425  revolutions  per  minute. 

Small  motors  are  usually  constructed 
with  two  field  magnet  poles,  or  belong  to 


^ 


«' 


THE  TRANSMISSION! 


PO* 


:•'> 


C 


the  bipolar  type.  Beyono^a^fepr^ain  size, 
however,  say  20-horse-power,  n>is  u&tialljr 
more  convenient  and  economical  to  con- 


FlG.    51. — QUADRIPOLAR    MOTOR. 

struct  motors  with  four  or  more  poles, 
<|iiadripolar  motors  being  common  be- 
tween 20-HP  and  500-HR 


198 


THE    ELECTRIC    MOTOR   AND 


A  form  of  quadripolar  motor  is  shown 
in  Fig.  51.  Here  there  are  four  magnets, 
M,  M,  M,  M,  and,  consequently,  four  rnag- 


FIG.  52. — QuADiuroLAii  MOTOK. 

netic  circuits  through  the  armature. 
There  are  also  four  sets  of  brushes,  instead 
of  two,  as  in  bipolar  machines,  but  oppo- 


THE   TRANSMISSION    OF   POWER.          199 

site  sets  of  brushes  are  connected  together 
electrically,  thus  making  a  single  pair  of 
main  terminals. 

Another  type  of  quadripolar  motor  is 
shown  in  Fig.  52.  Here  only  two  sets  of 
brushes  are  employed,  the  winding  and 
connection  of  the  armature  coils  being 
such  as  to  permit  the  use  of  two,  instead 
of  four  brushes. 


CHAPTER  VII. 

INSTALLATION    AND    OPERATION    OF    MOTORS. 

THE  installation  of  a  small  motor  does 
not  require  any  particular  preparation. 
It  is  only  necessary  to  bolt  the  base  frame 
of  the  motor  to  the  floor,  and  set  the 
machine  upon  it.  With  heavy  motors, 
however,  suitable  foundations  are  neces- 
sary in  order  to  support  them  securely. 
In  most  cases  a  belt  tightener  is  employed, 
whereby  the  tension  of  the  belt  can  be 
adjusted  by  sliding  the  motor  along  its 
bed  plate.  This  is  represented  in  Figs.  51 
and  52,  where  the  handle  H,  enables  this 
adjustment  to  be  made  readily.  Belts 
should  not  be  tightened  so  far  as  to  add 


200 


THE   TRANSMISSION    OF   POWER.          201 

considerably  to  the  friction  of  the  shaft 
in  its  bearings,  nor  be  left  so  loose  as  to 
slip  or  flap. 

Where  steady  driving  under  all  varia- 
tions of  load  is  a  matter  of  importance, 
the  shunt- wound  motor ;  or,  in  some  cases, 
the  compound-wound  motor,  is  employed, 
and,  in  fact,  series- wound  stationary  motors 
are  usually  only  employed  in  small  sizes 
such  as  in  fan  motors. 

By  reference  to  the  connections  of  the 
shunt-wound  motor  shown  in  Fig.  26,  it 
will  be  seen  that  the  armature  is  connected 
directly  across  the  mains.  If  we  assume 
that  this  connection  is  made  with  the 
armature  at  rest,  and  after  the  field  circuit 
has  been  closed,  so  as  to  excite  the  field 
and  produce  the  magnetic  flux  through 
the  armature ;  then,  since  the  resistance 


202 


THE   ELECTRIC    MOTOR   AND 


of  the  armature  is  necessarily  small,  a 
very  powerful  current  will  tend  to  flow 
through  the  armature,  owing  to  the 
absence  of  any  C.  E.  M.  F.  due  to  rota- 


FIG.  53. — STARTING  RHEOSTAT. 

tion.  This  first  inrush  of  current  and 
violent  resulting  torque,  are  apt  to  be 
injurious  to  the  motor.  When,  therefore, 
a  shunt- wound  motor  is  started  from  rest, 
it  is  necessary  to  insert  a  resistance  in  the 


THE   TRANSMISSION    OF   POWER. 


203 


armature  circuit,  so  as  to  limit  the  amount 
of  current  which  shall  pass  through  the 
armature  until  it  has  been  brought  up  to 
speed  and  enabled  to  produce  a  suffi- 


FIG.  54. — STARTING  RHEOSTAT. 

ciently  powerful  C.  E.  M.  F.  Such  adjust- 
able resistances  are  called  starting  rheo- 
stats. They  consist  essentially  of  coils  of 
wire,  usually  of  iron,  mounted  in  a  suit- 


204 


THE   ELECTRIC   MOTOR   AND 


able  frame,  and  connected  with  contact 
strips  in  such  a  manner  as  to  permit  their 
ready  insertion  or  removal  from  the  circuit 
by  the  movement  of  a  handle. 


FIG.  55. — STARTING  RHEOSTAT. 

A  form  of  starting  rheostat  is  shown 
in  Fig.  53.  Here  coils  of  iron  wire  are 
mounted  on  a  suitable  frame  and  con- 
nected in  series.  By  turning  the  switch 
S,  over  the  contact  points,  a  greater  or 
smaller  number  of  these  coils  may  be 


THE  TRANSMISSION   OF  POWER.          205 


FIG.  56.— INSTALLATION  OF  SHUNT-WOUND  MOTOR. 


&06  THE   ELECTRIC   MOTOR   ANJD 

included  in  the  circuit.  When  the  switch 
is  on  the  extreme  left  contact  point,  no 
coils  are  in  circuit,  and  when  on  the 
extreme  right,  all  are  in  circuit.  Fig.  54 
shows  a  different  type  of  starting  rheostat 
intended  for  use  with  small  motors.  Here 
the  resistance  wire  is  imbedded  in  a  suit- 
able enamel  on  the  lower  surface  of  the 
cast-iron  plate  shown,  and  the  switch 
serves,  as  before,  to  include  more  or  less 
of  this  wire  between  the  terminals.  Fig. 
55,  shows  a  similar  apparatus  of  larger 
sizes  intended  for  use  with  more  power- 
ful motors. 

Fig.  56  shows,  in  perspective,  the  ordi- 
nary method  of  installing  a  shunt-wound 
motor,  and  Fig.  57,  the  diagrammatic  con- 
nections of  the  same.  Similar  letters  refer 
to  similar  parts  in  both  figures.  It  will 
be  observed  that  a  pair  of  mains  MM,  and 


THE  TRANSMISSION   OF   POWER. 


207 


M'  M ',  being  connected  with  a  constant 
pressure  of,  say  110,  220,  or  500  volts,  ac- 
cording to  the  circuit,  and  the  winding 


M*  P.P.  CUTOUT  BOX 


d 

FIG.  57.— CONNECTIONS  OF  SHUNT- WOUND  MOTOB. 

of  the  motor,  are  connected  with  the  motor 
tli rough  the  switch  S,  and  the  cut-out  box 
T.  The  switch  S,  consists  of  a  handle  at- 


208  THE   ELECTRIC   MOTOR   AND 

tached  to  a  pair  of  copper  knife  Wades, 
in  such  a  manner,  that  on  depressing  the 
handle,  electrical  connection  is  secured  be- 
tween the  branch  mains  m,  m,  and  the  wires 
a  and  &,  leading  to  the  motor,  while  if  the 
handle  be  raised,  connection  is  instantly 
broken.  The  switch  is  called  a  double- 
pole  switch,  because  it  breaks  contact 
both  on  the  positive  and  negative  sides  of 
the  circuit ;  i.  <?.,  on  one  side,  at  each  knife 
edge.  The  cut-out  box  T,  contains  a  pair 
of  safety  fuses  of  lead  wires,  having  such 
an  area  of  cross  section  and  resistance, 
that  they  will  melt  if  the  motor  should 
receive  an  abnormal  amount  of  current. 

In  order  to  start  the  motor  from  rest,  it 
is  usual  to  throw  oft'  the  load  in  the  driv- 
ing machinery,  as  far  as  possible,  so  as  to 
reduce  the  resisting  torque  on  the  motor  as 
far  as  may  be  convenient.  The  handle  H, 


THE   TRANSMISSION    OF   POWER.  209 

of  the  rheostat  _/?,  is  then  so  turned  as  to 
cut  off  the  current  or  disconnect  its  circuit 
entirely.  Under  these  circumstances,  when 
the  switch  /SJ  is  thrown,  so  as  to  complete 
connection  between  the  wires  a  and  m,  on 
one  side,  say  the  positive  side,  and  b  and 
m',  on  the  negative  side,  then  a  compara- 
tively feeble  current  will  pass  through  the 
field-magnet  coils  6r,  6r,  and  steadily  excite 
them,  this  current  being  determined  by 
the  resistance  of  the  coils  and  the  pressure 
of  the  circuit.  If  now  the  handle  H,  be 
turned  slowly  so  as  to  close  the  armature 
circuit  through  all  the  resistance  in  the 
rheostat,  a  current  will  pass  through  the 
wires  b,  c,  the  rheostat  c/,  and  armature  a, 
and  this  current  will  start  the  motor  from 
rest,  provided  the  resisting  torque  is  not 
too  great. 

As   the  armature  accelerates,  the  resist- 


210  THE   ELECTRIC    MOTOR   AND 

ance  in  the  rheostat  is  cut  out,  and,  when 
the  motor  reaches  full  speed,  the  handle  is 
turned  so  as  to  cut  out  all  the  resistance. 
In  order  to  stop  the  motor,  the  reverse 
operations  are  effected ;  namely,  the  rheo- 
stat handle  is  turned,  without,  however, 
pausing  for  the  slacking  of  the  armature 
speed  until  the  current  is  entirely  cut  off 
the  armature.  The  switch  S,  is  then 
opened  so  as  to  cut  off  the  motor  fields, 
and  the  motor  is  thus  entirely  disconnected 
from  the  circuit.  In  some  cases,  when  the 
speed  of  the  motor  has  to  be  adjusted,  a 
separate  rheostat,  called  a  field  rheostat,  is 
inserted  in  the  circuit  of  the  field  coils  C\  C, 
and  out  of  the  path  of  the  armature  cur- 
rent. By  altering  the  resistance  in  the 
field-magnet  circuit,  within  proper  limits, 
the  current  strength  passing  through  these, 
being  controlled  by  Ohm's  law,  will  vary 
the  amount  of  flux  passing  through  the 


THE   TRANSMISSION   OF   POWER.          211 

magnetic  circuit  including  the  armature, 
and  force  the  latter  to  vary  its  speed  in 
order  to  maintain  a  constant  C.  E.  M.  F. 


FIG.  58. — ADJUSTMENT  OF  BRUSHES  ON  A  COMMUTATOR. 

The  correct  position  of  a  pair  of  brushes 
resting  on  a  bipolar  commutator  is  shown 
in  Fig.  58  at  A.  If  we  suppose  that  this 


212  THE   ELECTRIC   MOTOR   AND 

is  the  position  of  sparJdess  commutation; 
i.  e.,  the  position  at  which  the  brushes  will 
pass  current  into  the  armature  with  the 
least  sparking,  then,  as  the  load  is  gradu- 
ally applied  to  the  motor,  and  it  performs 
more  and  more  work,  it  is  usually  found 
that  the  brushes  have  to  be  shifted  back- 
ward, or  in  the  opposite  direction  to  that 
in  which  the  motor  is  moving,  in  order  to 
preserve  sparkless  commutation.  When 
the  machine  is  acting  as  a  generator,  a 
forward  lead  of  the  brushes  becomes  neces- 
sary, with  increase  of  load,  as  at  B, 
whereas,  when  employed  as  a  motor  taking 
current  from  the  mains,  instead  of  supply- 
ing current  to  the  mains,  the  lead  of  the 
brushes  is  backward  as  at  C.  In  the  most 
recent  types  of  well  designed  motors,  how- 
ever, the  sparking  at  the  commutator  is  so 
slight  at  full  load  that  no  shifting  of  the 
brushes  is  necessary. 


PROPERTY  C 

THE  TRANSMISSION   OfhfrR.         213 


We  have  already  referred  to 
ciency  of  the  motor  ;  namely,  to  the  ratio 
existing  between  the  mechanical  activ- 
ity it  develops  at  its  pulley,  and  the  electric 
activity  it  absorbs  at  its  terminals.  The 
losses  which  occur  in  the  motor  are  all  of 
a  frictional  nature,  but  may  be  divided 
into: 

(1)  Mechanical  frictions. 

(2)  Magnetic  frictions. 

(3)  Electric  frictions. 

Mechanical  frictions  are  those  which  are 
produced  at  the  bearings,  brushes  and  in 
air  churning.  The  magnetic  frictions  are 
those  which  occur  during  the  rotation  of 
the  armature  in  the  flux,  and  the  conse- 
quent rapid  reversal  of  the  magnetism  in 
its  core.  It  is  found  that  when  iron  has 
its  magnetism  reversed,  there  is  a  certain 
amount  of  energy  expended  in  the  iron  at 


214  THE   ELECTRIC   MOTOR   AND 

each  reversal.  The  more  powerful  the  mag- 
netism the  greater  will  be  the  expenditure 
of  energy  in  every  cubic  centimetre  or  cubic 
inch  of  iron  per  reversal.  The  energy 
takes  the  form  of  heat,  so  that  when  we 
rapidly  reverse  the  magnetic  flux  in  a  piece 
of  iron  or  steel  we  heat  it  even  though  no 
friction  in  the  mechanical  sense  occurs. 
This  loss  of  energy  by  magnetic  friction 
is  called  loss  of  energy  by  hysteresis,  or 
hysteretic  loss  of  energy.  The  more  power- 
ful the  magnetic  flux  through  the  arma- 
ture ;  the  more  rapid  the  rotation,  and  the 
greater  the  number  of  poles,  the  greater 
will  be  the  hysteretic  loss  of  energy,  In  a 
bipolar  field,  all  the  iron  in  the  armature 
core  reverses  the  direction  of  its  magnetic 
flux  twice  in  each  revolution.  In  a  quadri- 
polar  field  it  reverses  four  times  in  a  revo- 
lution, and  so  on. 

Thus,  referring  to  Fig.   25,  it  will  be 


THE   TRANSMISSION   OF   POWER.          215 

observed  that  the  armature  A,  is  magnet- 
ized by  the  flux  passing  through  it  in  the 
direction  of  the  flux,  having  north  polarity 
over  the  surface  opposing  the  field  pole  S, 
where  the  flux  emerges,  and  south  polarity 
where  the  flux  enters,  over  the  surface 
opposite  the  field  pole  N.  After  the 
armature  has  made  half  a  revolution,  the 
direction  of  magnetism  in  its  mass  will  be 
reversed,  the  part  marked  n,  in  the  figure 
then  becoming  the  part  marked  s,  and 
vice  versa.  It  is  this  reversal  of  mag- 
netism which  gives  rise  to  hysteresis,  and 
the  more  powerful  the  magnetic  intensity 
in  the  armature  which  has  to  be  reversed, 
the  greater  the  hysteretic  loss. 

Electrical  friction  is  due  either  to  eddy 
currents,  or  stray  currents  set  up  by  dy- 
namo action  in  the  mass  of  the  conductor, 
armature  core,  or  field  poles  ;  or,  to  the 


216  THE   ELECTRIC    MOTOR. 

ordinary  thermal  expenditure  of  energy  by 
the  passage  of  the  armature  currents  and 
field  currents  through  their  respective 
windings.  If,  for  example,  the  field  coils 
of  a  motor  take  a  current  of  3  amperes 
steadily,  to  excite  them  'from  mains  at  a 
pressure  of  110  volts,  then  they  will  expend, 
in  heating  the  field  coils,  an  activity  of  330 
watts  continuously. 


CHAPTER  VIII. 

ELECTRIC    TRANSMISSION    OF    POWER. 

THE  high  efficiency,  low  cost,  and  com- 
parative ease  with  which  the  electric 
motor  can  be  controlled  as  to  speed  and 
power ;  the  fact  that  it  can  be  made  to 
automatically  regulate  the  current  it  re- 
quires ;  and  its  cleanliness,  noiselessness, 
safety,  compactness  and  portability,  cause 
it  to  stand  to-day  in  these  respects  un- 
rivalled as  a  prime  mover.  Not  only,  how- 
ever, does  the  electric  motor  possess  these 
points  of  excellence  far  in  excess  of  other 
prime  movers,  but  it  also  possesses  special 
advantages  in  the  field  of  long  distance 
transmission  of  power. 


217 


218  THE   ELECTRIC    MOTOR   AND 

It  will  be  interesting  to  discuss  the 
electric  motor  in  this  respect  aod  to  ex- 
amine the  conditions  under  which  power 
can  be  transmitted  over  considerable  dis- 
tances. Suppose,  for  example,  that  it  is 
desired  to  furnish,  at  a  distant  point,  a 
steady  activity  of  50  horse-power,  for  10 
hours  a  day.  This  power  may  be  em- 
ployed, for  example,  to  drive  the  machin- 
ery in  a  factory.  We  can  either  put  a 
steam  engine  in  the  factory,  or  install  there 
an  electric  motor,  drive  a  generator  at 
some  distant  point,  from  a  water-power  or 
steam  engine,  and  connect  the  generator 
with  the  motor  by  insulated  electric  con- 
ductors. 

A  system  for  the  distribution  of  electric 
energy  is  represented  in  Fig.  59,  where  6?, 
is  the  generator,  situated  at  the  source  of 
power.  M,  is  the  motor  at  the  factory, 


THE   TRANSMISSION    OF   POWER.  219 

or  point  where  the  power  is  to  be  de- 
livered, and  ab,  cd,  are  the  wires  connect- 
ing the  two  places.  It  is  theoretically 
possible  to  employ  only  one  wire,  using  the 
earth  as  a  return  conductor,  as  in  teleg- 
raphy, but  in  practice,  this  arrangement 
has  never  been  found  satisfactory  for  the 


FIG.  59.— TYPICAL  ELECTRIC  TRANSMISSION  SYSTEM. 

transmission  of  power,  and  two  conductors 
are  always  employed. 

The  distance  between  6r  and  M,  the 
generator  and  motor,  that  is  between  the 
points  of  supply  and  delivery,  may  vary 
from  a  few  feet  to  many  miles,  In 


220  THE   ELECTRIC    MOTOR   AND 

factories,  power  is  distributed  from  one 
building  to  another,  or  from  different 
parts  of  the  same  building  by  means  of 
belts  and  counter-shafting.  The  friction 
of  such  belts  and  shafts  when  long,  may 
represent  a  considerable  waste  of  power, 
so  that  it  is  often  much  more  economical 
to  restrict  the  counter-shafts  to  short 
lengths,  each  operated  by  a  separate 
motor,  and  distribute  the  power  from  a 
single  central  source,  or  poiver  "house,  to  all 
these  motors,  as  secondary  centres  of  dis- 
tribution. In  such  cases  the  transmission 
lines  may  be  only  a  few  hundred  feet  in 
length. 

In  cities,  where  electric  central  stations 
have  been  constructed,  the  demand  for 
power,  either  for  industrial  or  domestic 
uses,  may  be  supplied  by  motors  operated 
on  electric  circuits  consisting  of  the  street 


THE  TRANSMISSION   OF  POWER.         221 

mains.  In  such  cases,  the  distributing  cir- 
cuits may  be  one  or  two  miles  in  length. 
Finally,  cases  may  occur  where  power  can 
be  developed  under  specially  economical 
advantages,  at  particular  localities ;  as,  for 
example,  at  a  waterfall,  where  turbines 
are  installed,  and  thus  cheap  power  may 
be  transmitted  to  a  distant  city  at  a  cost 
which  may  be  less  than  that  of  producing 
the  power  in  that  city  by  the  steam 
engine.  In  some  cases,  the  distance  to 
which  the  powrer  may  be  transmitted  may 
be  many  miles. 

Systems  of  electric  transmission  of 
power  are,  to-day,  in  fairly  extended  use. 
Moreover,  this  use  is  found  in  practice  to  be 
so  satisfactory  that  it  is  rapidly  increasing. 

The  greatest  distance  to  which  power 
has  been  electrically  carried  in  any  large 


THE   ELECTRIC   MOTOR   AND 

quantity  is  109  miles,  which  is  the  dis- 
tance between  the  river  Neckar  at  Lauffen, 
Germany,  and  the  city  of  Frankfort. 
During  the  Frankfort  Electric  Exhibition 
of  1891,  about  200  horse-power  was 
steadily  transmitted  from  turbines  driven 
at  Lauffen  to  the  Exhibition  Building  at 
Frankfort. 

The  longest  electric  power  transmission 
circuit  operating  commercially  at  the 
present  day  is  at  the  San  Joaquin  valley  to 
Fresno,  Cal.,  over  a  distance  of  35  miles,  at 
an  alternating-current  pressure  (triphase)  of 
11,200  volts  between  cond  uc tors.  The  next 
longest  circuit  in  the  United  States  is  from 
Folsom  to  Sacramento,  Cal.,  a  distance  of  24 
miles,  transmitting  3,000  HP.  at  11,500  volts 
alternating  triphase  pressure.  The  longest 
circuit  in  Europe  is  from  Tivoli  to  Rome, 
a  distance  of  18  miles  at  an  alternating- 


THE   TRANSMISSION   OF   POWER.          223 

current  Uniphase  pressure  of  5,000  volts. 
This  system  has  been  installed  three  years. 

We  propose  to  examine  the  conditions 
which  affect  the  problem  commercially. 
Assuming  that  the  50-horse-power  con- 
tinuous-current motor  installed  in  the  fac- 
tory above  referred  to,  may  be  wound  for 
any  desired  pressure,  and  will  possess, 
when  so  wound,  an  efficiency  of  90  per 
cent.,  then  the  electric  horse-power  which 
must  be  supplied  to  its  terminals,  in  order 
to  maintain  a  steady  mechanical  activity, 

50 
will  be,  T;      =  55.55  horse-power  =  55.55 

\).J 

X  746  =  41,440  watts  =  41.44  KW. 
This  electric  activity  could  be  supplied  as 
41,440  amperes  at  a  pressure  of  1  volt,  in 
which  case  the  motor  would  have  to  be 
wound  for  1  volt ;  or,  as  20,000  amperes 
at  a  pressure  of  2.072  volts ;  or,  as  1,000 


224  THE    ELECTRIC   MOTOR   AND 

amperes  at  a  pressure  of  41.44  volts ;  or, 
100  amperes  at  a  pressure  of  414.4  volts; 
or,  10  amperes  at  a  pressure  of  4,144  volts. 
In  each  case,  the  motor  would  have  to  he 
wound  for  the  required  pressure. 

Let  us  suppose  that  the  cost  of  winding 
the  motor  is  the  same  whatever  pressure 
might  be  employed.  This  would  not  be 
strictly  true,  since  the  winding  for  either  a 
very  low  pressure,  or  a  very  high  pressure 
motor  would  be  comparatively  expensive ; 
but,  within  a  certain  range,  say  from  50 
volts  to  1,000  volts,  the  cost  would,  prob- 
ably, be  nearly  the  same.  Similarly,  the 
cost  of  winding  the  generator  for  any  pres- 
sure may  be  considered  at  present  as  con- 
stant. Let  us  also  suppose  that  a  certain 
loss  of  power  is  allowed  in  the  transmission 
lines  or  conductors,  say  10  per  cent,  of  the 
full-load  power  developed  at  generator  ter- 


THE  TRANSMISSION   OF   POWER.          225 

minals.     The  efficiency  of  the  line  being, 
therefore,  ~,  the  power  to  be  supplied  at 

the  generator  terminals  would  be  4^'44 

0.9 
46.04  KW. 

We  then  have  an  unwound  generator  at 
the  transmitting  end  of  the  line,  whose 
output,  at  full  load,  must  be  46.04  KW, 
an  unwound  motor  at  the  factory,  or 
receiving  end  of  the  line,  whose  intake 
must  be  41.44  KW,  and  whose  output 
will  be  50  horse-power,  or  37.3  KW. 
The  size  of  the  conductors  between  these 
two  points  remains  to  be  determined. 

Let  us  suppose  that  the  distance 
between  these  two  stations  is  5  miles; 
then  the  total  length  of  circuit  will  be  10 
miles,  including  the  outgoing  and  return- 
ing conductors.  In  order  that  the  loss  of 


226  THE   ELECTRIC   MOTOR   AND 

activity  iri  the  resistance  of  these  10  miles 
of  conducting  wire,  shall  as  above 
assumed,  be  10  per  cent,  of  the  activity 
supplied  at  the  generator  terminals,  it  is 
necessary  that  the  drop  of  pressure  pro- 
duced by  the  working  current  in  these  10 
miles,  shall  be  10  per  cent,  of  the  pressure 
at  the  generator  terminals.  Thus,  if  the 
pressure  at  generator  terminals  be  500 
volts,  and  the  pressure  at  the  motor  termi- 
nals 450  volts,  then  the  drop  of  pressure 
in  the  line  will  be  50  volts,  or  10  per  cent, 
of  that  at  generator  terminals,  and  the 
activity  expended  in  heating  the  resistance 
of  the  line  wires  will  be,  in  watts, 
50  volts  x  working  current  in  amperes, 

while    the    activity    expended    in    the 

motor  will  be 
450   volts  x  working  current  in  amperes, 

the  total  activity  of  the  generator,  being, 
500  volts  x  working  current  in  amperes. 


THE  TRANSMISSION   OF  POWER.         227 

If  then,  we  wind  the  generator  for  10 
volts,  and  the  motor  for  9  volts,  we  lose  10 
per  cent,  of  our  electric  activity  in  the 

line,  but  the  current  must  be— ^-  -  =  4,604 

amperes,  and  the  drop  in  the  two  lines 
together,  one  volt,  or  half  a  volt  in  each. 
The  resistance  of  the  two  lines  together 

must,  therefore,  be  -  — —  ohm,  and  the  re- 
4,604 

sistance  per  mile  must  be  T/rth  of  this,  or 

4fi  040  ohm.     Ordinary  trolley  wire,  No.  0 

A.  W.  G.,  has  a  resistance  of,  approx- 
imately, half  an  ohm  per  mile.  Conse- 
quently, the  size  of  conductor,  which 
would  have  to  be  employed  in  order  to  have 

only  ohm  per  mile,  wrould  have  to 

be  -        -  =  23,020  times  as  heavy,  or  as 


228  THE    ELECTRIC    MOTOR   AND 

large  in  cross-section.  Such  an  enormous 
conductor  would  be  prohibitively  costly 
and,  therefore,  such  a  system  of  transmis- 
sion could  not  be  carried  out  in  practice. 

If  now,  the  generator  were  wound  for 
100  volts,  and  the  motor  for  90  volts, 
representing  a  drop  in  the  transmission 
line  of  10  volts,  or  5  volts  in  each  wire, 
the  current  strength  in  the  circuit  would 

be  -  _  460.4  amperes.     The    resist- 

ance of  conductor,  which  would  produce  a 
drop  of  10  volts  with  this  current  would 

10  I 

be  TTVTTT  ohm  =-  r^7  °"m>  and  this  being 

the  resistance   of    10  miles  of   conductor, 

the  resistance  per  mile  should   be  •     ..   - 

460.4 

ohm.  If  we  assume  the  resistance  of  a 
trolley  wire,  as  before,  to  be  exactly  half 


THE  TRANSMISSION   OF   POWER.          229 

an  ohm,  the  size  of  the  conductor  rieces- 

460  4 

sary    would   be  equal  to  -  =    230.2 

2 

trolley  wires  iu  cross-sectiou  or  weight. 

By  increasing  the  pressure  of  trans- 
mission ten  times ;  namely,  from  10  volts  to 
100  volts,  we  have  reduced  by  100  times 
the  size  of  wire,  which  is  necessary  in 
order  to  transmit  a  given  activity  of  50 
horse-power  with  a  fixed  percentage  of 
loss,  because  we  have  reduced  the  current 
strength  ten  times,  and  we  have  increased 
the  permissible  drop  in  the  circuit  from  1 
volt  to  10  volts,  so  that  the  resistance  has 
been  increased  100  times. 


In  the  same  way,  if  the  generator  be 
wound  for  1,000  volts,  and  the  motor  for 
900  volts,  allowing  10  per  cent,  drop  in 
transmission  lines,  as  before,  the  current 


230  THE   ELECTRIC    MOTOR  AND 

strength  necessary  to  deliver  46,040  watts 
at    the     generator     terminals     will      be 

-y-^  -  =  46.04  amperes,  and  the  resistance 

which  will  have  to  exist  in  the  two  trans- 
mission lines,  in  order  to  produce  with  this 

current  a  drop  of  100  volts,  will  be 


9  i  >TO 

2.173    ohms;    or,    tT7T~  ~  0.217    ohm   per 

mile.  If  we  assume  that  the  trolley  wire 
has  just  0.5  ohm  per  mile,  then  the  size  of 
the  wire  necessary  to  employ  between  the 

generator   and   motor   will   be   —  --      — 

0.2173 

2.302  times  that  of  trolley  wire.  Roughly 
speaking,  therefore,  the  size  of  the  wire 
would  only  be  twice  that  of  the  trolley 
wire.  That  is,  for  a  loss  of  10  per  cent,  or 
4.604  KW.  in  transmission  the  size  of 
wire  for 


THE   TRANSMISSION    OF   POWER.          231 

10  volts  at  generator  terminals,  and  9  at 

motor    terminals,   would     have    to     be 

23,020  times  trolley  wire. 
100  volts  at  generator  terminals   and   90 

at  motor  terminals,  230.2  times  trolley 

wire. 
1,000  volts  at  generator  terminals  and  900 

at  motor  terminals,  2.302   times  trolley 

wire. 
10,000    volts  at  generator    terminals   and 

9,000  at  motor  terminals,  0.02303  times 

trolley  wire. 

In  other  words,  the  cost  of  copper 
required  for  a  given  distance  and  given 
loss  in  transmission  varies  inversely  as  the 
square  of  the  electric  pressure. 

We  have  hitherto  assumed  that  the  dis- 
tance between  the  generator  and  the  motor 
was  5  miles.  Let  us  now  suppose  that 


232  THE   ELECTRIC   MOTOR   AND 

this  distance  is  doubled,  or  changed  to  10 
miles,  and  that  the  length  of  the  circuit  is, 
consequently,  changed  to  20  miles.  If, 
as  before,  10  per  cent,  of  the  electric  ac- 
tivity has  to  be  expended  in  the  resistance 
of  the  circuit,  then  the  same  number  of 
volts  drop  will  have  to  be  developed  in  20 
miles,  which  previously  were  developed  in 
10,  so  that  the  resistance  per  mile  of  the 
conductor  must  be  halved  for  any  given 
pressure  at  generator  and  motor. 

Thus,  if  the  generator  be  wound  for 
1,000  volts  and  the  motor  for  900  volts, 
the  drop  in  the  transmission  lines  will  be 
100  volts,  as  before.  The  current  will  be 
46.04  amperes,  and  the  resistance  of  the 

circuit  as  before  =  2.302  ohms,  and 

the  resistance  per  mile,  — th  of   this,    or 


THE  TRANSMISSION   OF   POWER.          238 

0.1151   ohm.  requiring   a  wire  _1^_1  — 

0.1151 

4.604  times  that  of  trolley  wire,  or  twice 
as  big  a  wire  as  when  the  circuit  was  only 
10  miles  in  length.  Moreover,  since  we 
have  to  provide  20  miles  of  this  double 
wire,  instead  of  10  miles,  it  is  evident  that 
the  total  weight  of  copper  conductor  will 
have  increased  four  times. 

Similarly,  it  will  readily  be  found  that 
if  we  trebled  the  distance  between  gener- 
ator and  motor  we  should  have  to  use  a 
wire  three  times  as  large  for  30  miles 
as  for  10  miles,  and  would,  therefore, 
require  9  times  the  total  weight  of  the 
copper  needed  in  the  first  instance.  In 
other  words,  the  total  weight  of  con- 
ductor required  in  a  transmission  system 
varies  with  the  square  of  the  distance  be- 
tween generator  and  motor  for  a  given 


234  THE   ELECTRIC   MOTOK  AND 

pressure  of  transmission,  and  for  a  given 
percentage  of  loss  of  activity.  In  order, 
therefore,  to  transmit  power  economically 
over  considerable  distance,  it  is  essential 
to  employ  high  electric  pressures,  since 
otherwise  the  cost  of  copper  becomes  pro- 
hibitive. 

In  building  and  winding  continuous- 
current  dynamo  machines,  whether  for 
motors  or  generators,  the  limit  of  pressure 
which  can  be  safely  employed,  depends 
upon  the  character  of  the  insulation  em- 
ployed in  the  winding,  and  upon  the 
nature  of  the  commutator.  The  commuta- 
tor is  obviously  a  weak  point  in  such 
machines,  since  the  full  electric  pressure 
has  to  be  maintained  between  the  brushes 
which  are  only  a  few  inches  apart,  and  are 
separated  by  only  a  few  strips  of  mica  on 
a  revolving  cylinder.  The  highest  electric 


THE  TRANSMISSION   OF   POWER.         235 

pressures  which  are  employed  in  dynamo 
machines  are  10,000  volts.  These  pres- 
sures, however,  are  only  employed  in  a  few 
generators  for  series  arc-light  circuits  and 
are  not  employed  in  motors.  The  highest 
pressures  for  which  motors  have  been 
built,  are  practically  2,000  volts,  while 
ordinarily  1,000  volts  is  the  limit  of  pres- 
sure in  motor  construction.  Consequently, 
under  the  conditions  imposed  by  the  art 
of  motor  building,  as  it  exists  to-day,  the 
limitations  of  distance  to  which  power  can 
be  transmitted  by  the  continuous  current 
are  those  which  are  prescribed  either  by 
the  cost  of  conductor,  or  by  the  cost  of 
power  wasted  in  conductors  at  this  limit- 
ing pressure  of  1,000  volts.  Moreover,  at 
pressures  exceeding  this  amount,  the  motors 
become  dangerous  to  handle  without  pre- 
cautions, since  the  shock  from  a  thousand 
volt  circuit  is  a  serious  one. 


236  THE   ELECTRIC    MOTOR   AND 

Assuming  that  the  amount  of  money 
which  must  be  expended  in  conductors 
to  transmit'  a  given  number  of  horse- 
power over  any  actual  distance,  at,  say 
1,000  volts  pressure,  is  not  excessive ;  or, 
in  other  words,  that  it  will  pay  to  employ 
continuous-current  electric  transmission 
under  these  conditions,  the  question  next 
arises,  What  should  be  the  percentage  of 
drop  allowed  in  the  line  ?  If  we  employ 
a  large  percentage  of  drop  we  reduce 
the  size  and  cost  of  the  copper  con- 
ductors, but  at  the  same  time  we  waste 
more  activity  in  the  conductors,  which 
wasted  activity  has  a  money  value.  At 
what  point  then  should  the  drop  be  fixed 
so  as  to  secure  the  maximum  economy  ? 

In  practice  the  solution  to  this  problem 
can  only  be  determined  by  making  actual 
estimates  with  different  percentages  of 


THE  TRANSMISSION    OF   POWER.          237 

drop.  For  example,  if  the  distance  be- 
tween generator  and  motor  be  1  mile, 
and  the  pressure  at  the  generator  terminals 
1,000  volts,  then  the  problem  is  to  deter- 
mine what  shall  be  the  most  economical 
drop  to  employ  in  the  line  conductors.  It 
is  evident  that  the  amount  of  power  to  be 
transmitted  does  not  enter  directly  into 
this  question,  because,  if  we  double  the 
power  transmitted,  we  marely  double  the 
whole  transmission  system,  including  gener- 
ator, wires  and  motors,  so  that  we  may,  for 
convenience,  simply  consider  the  transmis- 
sion of  one  horse-power.  Let  us  suppose 
that  1  KW  capacity  in  motors  costs  say 
$40  when  installed,  so  that  1,000  KW  maxi- 
mum mechanical  delivery  at  the  motor 
shaft  costs  $40,000  in  motor  machinery. 
Then,  if  the  efficiency  of  the  motor  be 
taken,  at  say  90  per  cent.,  which  would 
be  a  fair  value  for  moderately  large  sizes 


238  THE   ELECTRIC   MOTOR   AND 

of  motors,  the  electric  activity  at  motor 
terminals,  per  KW  delivery  at  belt,  would 
be  1.111  KW.  If  now,  a  size  of  wire 
which  would  expend  in  resistance  at  the 
working  pressure  10  per  cent,  of  the 
maximum  pressure  employed,  the  total 
activity  at  the  generator  terminals  would 
be  1.235  KW  and  the  power  delivered 
to  the  generator  shaft  assuming  90  per 

cent,  efficiency  would  be KW  = 

0.9 

1.372  KW.  Consequently,  we  have,  under 
these  conditions,  to  supply  1.372  KW 
to  the  generator  shaft  in  order  to 
obtain  1  KW  from  the  motor  shaft.  The 
total  annual  charge  of  the  system  will  be 
the  interest  and  depreciation  on  the  invest- 
ment, added  to  the  cost  of  superintendence 
and  repairs  and  the  cost  of  the  power 
supplied  at  the  generator  shaft.  If  the 
power  be  obtained  from  a  waterfall,  which 


THE   T&ANSMISSION   OF   POWER.          239 

is  not  limited  in  supply,  then  a  little  extra 
loss  of  power  in  the  line  will  not  be  a 
matter  of  serious  consequence,  since  it  will 
only  involve  the  use  of  a  correspondingly 
larger  generator  and  turbine,  so  that  the 
cost  will  only  be  increased  by  the  fixed 
charges  on  the  extra  investment.  If,  how- 
ever, the  power  to  be  transmitted  is  from  a 
steam  plant,  not  only  will  the  engines  and 
boilers  and  generators  at  the  transmitting 
end  have  to  be  larger,  by  reason  of  a 
greater  waste  of  power  in  the  line,  but  also 
the  coal  consumed  at  the  generating  end 
will  be  increased.  We,  have,  therefore,  to 
find  by  trial  and  estimate  such  a  size  of  wire 
as  will  make  the  total  annual  cost  of  the 
power  delivered  a  minimum.  If  we  make 
the  wire  too  small  and  its  resistance  too 
great,  its  first  cost  will  be  reduced  and  the 
annual  interest  on  the  wire  will  be  reduced. 
There  will  practically  be  no  depreciation 


240  THE  ELECTRIC   MOTOR. 

on  copper  wire,  although  there  will  be 
some  depreciation  on  the  poles,  supports  or 
insulation  which  must  be  maintained  about 
the  wire.  On  the  other  hand,  the  engines, 
boilers  and  generators  will  cost  more,  and 
the  coal  per  horse-power  hour,  or  per  KW 
hour,  delivered  will  cost  more.  If  we 
make  the  wire  too  large,  we  reduce  the 
cost  of  coal  in  the  generating  station,  and 
also  the  fixed  annual  charges  of  interest, 
depreciation,  superintendence  and  repairs 
on  generating  plant  which  is  now  smaller, 
but  we  have  an  increase  in  the  fixed 
charges  upon  the  greater  investment  in  the 
line  conductors.  Economy  requires  that 
the  total  charges  or  total  annual  expense 
shall  be  as  small  as  possible,  and,  con- 
sequently, the  size  of  the  wire  must  be  so 
chosen  that  under  the  estimated  conditions 
of  load  the  total  cost  of  wire,  power  and 
generating  apparatus  shall  be  a  minimum. 


PROPERTY  OF 


CHAPTER  IX. 

ALTERNATING -CURRENT    MOTORS. 

CONSIDERABLE  attention  has  been  paid 
of  recent  years  to  the  development  of 
alternating-current  machinery,  owing  to 
the  facilities  which  such  machinery  pos- 
sesses for  the  long-distance  transmission 
of  power.  While  it  will  be  necessary  to 
refer  briefly  to  the  differences  between  the 
alternating  and  continuous  current,  space 
will  not  permit  the  discussion  of  the 
peculiarities  of  alternating  currents  to  any 
great  length,  and  the  reader  is  therefore 
referred  to  the  authors'  volume  on  "Alter- 
nating Electric  Currents,"  in  the  Ele- 
mentary Electro-Technical  Series,  for  more 
complete  particulars  in  that  direction. 


241 


242  THE   ELECTRIC   MOTOR  AND 

A  continuous  E.  M.  F.,  that  is  ati 
E.  M.  F.  which  always  acts  in  the  same 
direction,  establishes,  or  tends  to  establish, 
a  continuous  electric  current  in  its  circuit. 
An  alternating  E.  M.  F.y  that  is  an 
E.  M.  F.  which  at  regular  successive  in- 
intervals  reverses  its  direction,  establishes, 
or  tends  to  establish,  an  alternating  current 
in  its  circuit.  A  continuous-current  cir- 
cuit has  its  analogue  in  a  reservoir,  which 
discharges  through  a  pipe  or  hydraulic 
conductor.  An  alternating-current  circuit 
has  its  analogue  in  a  hydraulic  circuit  in 
which  a  pump  drives  water  alternately 
backwards  and  forwards  at  regular  inter- 
vals. The  tidal  flow  in  a  river  is  another 
example  of  alternating  water  currents. 

A  complete  to-and-fro  motion  or  double 
alternation  constitutes  a  cycle.  The  num- 
ber of  cycles  per  second,  or  per  minute,  con- 


THE   TRANSMISSION    OF   POWER.          243 

stittites  what  is  called  the  frequency.  In 
commercial  practice  the  frequency  varies 
between  25  cycles  per  second,  or  50  rever- 
sals of  E.  M.  F.  and  current  per  second, 
(1,500  cycles  per  minute,  or  3,000  re- 
versals or  alternations  per  minute)  and  140 
cycles,  or  280  alternations  per  second, 
(8,400  cycles,  or  16,800  alternations  per 
minute). 

The  current  strength  in  an  alternating- 
current  circuit,  unlike  that  in  a  continu- 
ous-current circuit,  does  not  depend  only 
upon  the  E.  M.  F.  and  the  resistance  as 
related  by  Ohm's  law.  To  determine  the 
current  strength  in  alternating-current  cir- 
cuits, it  is  necessary  to  take  into  account  a 
new  quantity  called  reactance.  Reactance 
is  a  quantity  similar  to  resistance,  and  like 
it,  is  capable  of  being  expressed  in  ohms. 
Its  value  increases  directly  with  the  fre- 


244  THE    ELECTRIC    MOTOR    AND 

quency.  A  coil  of  wire,  for  example, 
either  with  01*  without  an  iron  core,  having 
a  resistance  of  3  ohms,  will  permit  a  cur- 
rent of  3  1/3  amperes  to  flow  through  it 
under  a  continuous  pressure  of  10  volts; 
but,  if  the  E.  M.  F.  applied  to  its  termi- 
nals, instead  of  being  continuous,  alter- 
nates with  a  frequency  of  say  50  cycles 
per  second,  the  coil  will  possess  not  only 
a  resistance  of  3  ohms,  but  a  reactance 
which  might  be,  at  this  frequency,  say  4 
ohms.  This  reactance  has  to  be  consid- 
ered as  to  its  effect  of  reducing  the  current 
strength.  If  the  frequency  were  doubled  ; 
that  is,  increased  to  100  cycles  per  second, 
or  200  reversals  of  E.  M.  F.  and  current 
per  second,  the  reactance  would  be 
doubled,  or  increased  to  8  ohms,  and  if 
the  frequency  were  made  150  cycles  per 
second,  the  reactance  would  be  increased 
to  12  ohms. 


THE   TRANSMISSION   OF   POWER.          245 

The  amount  of  the  reactance  depends 
not  only  upon  the  number  of  turns  in  the 
coil  but  also  on  their  ability  to  produce 
magnetic  flux  through  the  coil.  The 
greater  amount  of  magnetic  flux  which 
will  be  produced  by  the  current  in  passing 
through  the  coil,  the  greater  will  be  the 
reactance  of  the  coil  for  a  given  frequency. 
The  reactance  is  sometimes  described  as 
the  choking  effect  of  the  current,  since  it 
tends  to  check  or  choke  the  current  which 
flows ;  but  the  amount  of  this  choking, 
that  is  the  total  effective  resistance,  cannot 
be  determined  by  simply  adding  together 
the  resistance  and  reactance.  Thus,  in  the 
case  of  the  above  coil,  having  3  ohms 
resistance  and  4  ohms  reactance,  at  a 
frequency  of  50  cycles  per  second,  gener- 
ally represented  thus,  50~,  the  effective  re- 
sistance of  the  coil  will  not  be  7  ohms,  but 
can  be  obtained  by  drawing  the  resistance 


246  THE   ELECTRIC    MOTOR   AND 

as  the  base,  and  the  reactauce  as  the  per- 
pendicular of  a  right-angled  triangle  as 
in  Fig.  60.  The  combined  influence  of  re- 
actance and  resistance  will  then  be  repre- 


B 

A 


f 


IS 

IS 


V  RESISTANCE  3  OHMS        A 

FIG.  60. — DIAGRAMS    INDICATING    RELATION  OP  IMPED- 
ANCE TO  RESISTANCE  AND  REACTANCE. 

sented  by  the  length  of  the  hypothenuse 
OB,  which  in  this  case  will  be  5  ohms,  so 
that  the  current  strength  passing  through 
the  circuit  will  be  10  volts,  divided  by  5 
ohms  =  2  amperes. 


THE  TKANSMISSION    OF   POWER.  247 

Ohm's  law,  as  modified  for  alternating 
current  circuits,  is,  therefore, 

Volts  E.  M.  F. 
~  Ohms  Impedance. 

If  the  frequency  of  alternation  be  doubled, 
so  that  the  reactance  is  doubled,  or  be- 
comes 8  ohms,  the  impedance,  as  shown  in 
Fig.  61,  will  be  increased  to  8.544  ohms, 
and  the  current  strength  in  the  coil  will, 

therefore,  be  reduced  to  5-^7,   =  1.17    am- 

0.544 

peres.  If  the  frequency  of  alternation 
were  made  indefinitely  small,  so  that  the 
current  became  continuous,  the  impedance 
would  become  the  simple  resistance. 

Reactance  plays  a  prominent  part  in  all 
alternating-current  circuits.  It  is  usefully 
employed  in  apparatus  called  alternating- 
current  transformers,  which  consist  essen- 
tially of  coils  of  wire  wound  upon  a 


248  THE   ELECTRIC   MOTOR   AND 

common  core.     One  of  these  coils  is  con- 
nected with  the  driving  or  primary  circuit, 


O      RESISTANCE  $  OHMS    A 

FIG.  61. — DIAGRAM   INDICATING    RELATION   OF   IMPED- 
ANCE TO  REACTANCE. 

while  the  other  coil  is  connected  with  the 
driven  or  secondary  circuit ;  i.  e.,  the  circuit 


THE  TRANSMISSION    OF   POWER.          249 

to  which  the  activity  has  to  be  transferred. 
When  the  secondary  circuit  is  opened  and 
is,  therefore,  devoid  of  activity,  the  react- 
ance of  the  coil  in  the  primary  circuit  has 
a  maximum  value  depending  upon  the  fre- 
quency, the  number  of  turns,  and  their 
arrangement  upon  the  iron  core,  so  that 
the  impedence  of  the  primary  coil  has  a 
definite  and  usually  a  large  value  in  ohms. 
Consequently,  the  primary  coil  takes  a  very 
small  current  when  supplied  at  a  given 
pressure.  When,  however,  the  secondary 
circuit  is  closed  through  incandescent 
lamps,  motors,  or  other  devices,  the  effect  of 
the  activity,  which  is  thus  transferred  from 
the  primary  to  the  secondary  coil  is  to 
lower  the  reactance  of  the  primary  coil,  and 
thus  reduce  its  impedance,  permitting  a 
greater  current  strength  and  activity  to 
enter  the  primary  coil  from  its  supply 
mains. 


250  THE   ELECTRIC   MOTOR   AND 

An  alternating-current  transformer  is, 
therefore,  an  apparatus,  which,  without 
revolving  parts,  automatically  transfers 
energy  from  its  primary  to  its  secondary 
circuit.  At  the  same  time,  it  possesses  a 
very  valuable  property  of  transforming  the 
energy,  in  regard  to  pressure  and  current, 
in  a  manner  depending  upon  the  winding 
of  the  primary  and  secondary  coils.  If  the 
primary  and  secondary  coils  have  the  same 
size  and  the  same  number  of  turns,  the 
primary  and  secondary  E.  M.  F.'s  will  be 
practically  the  same,  but  if  the  primary 
winding  has,  say  10  times  the  number  of 
turns  as  in  the  secondary  winding,  the  E. 
M.  F.  acting  in  the  secondary  circuit  will  be 

TTjth  of  that  in  the  primary  circuit.      Such 

a  transformer  is  called  a  step-down  t/rans- 
former,  because  the  pressure  is  reduced 
in  the  secondary  circuit.  If,  however, 


THE  TRANSMISSION   OF   POWER.          251 

the  secondary  winding  has,  say  10  times  the 
number  of  turns  as  in  the  primary  wind- 
ing, the  secondary  E.  M.  F.  will  be  10  times 
as  great  as  the  primary  E.  M.  F.  and  the 
current  strength  will  be,  approximately, 

— rth   of    the    primary    current    strength. 

Such  a  transformer  is  called  a  step-up 
transformer,  because  it  effects  an  increase 
in  pressure  in  its  driving  circuit. 

It  is  obvious,  that  if  no  activity  were 
absorbed  in  a  transformer,  the  activity  in 
the  secondary  circuit  would  be  equal  to 
the  activity  received  by  the  transformer  at 
its  primary  terminals.  As  a  matter  of  fact, 
the  loss  in  a  transformer,  although  com- 
paratively small,  is  nevertheless  quite 
appreciable.  A  large  transformer  will 
deliver,  at  its  secondary  terminals,  about 
98  per  cent,  of  the  activity  it  receives  at  its 


252  THE   ELECTRIC   MOTOR   AND 

primary  terminals,  or  will  absorb  as  heat, 
about  2  per  cent,  of  its  maximum  received 
activity.  This  loss  of  2  per  cent,  will  be 
only  slightly  reduced  at  no  load,  or  on 
open  secondary  circuit,  so  that,  if  a  10 
KW  transformer ;  i.  <?.,  a  transformer  cap- 
able of  delivering  steadily  an  activity  of 
10  KW  in  its  secondary  circuit,  absorbs 
300  watts  at  full  load,  it  will  require  to  be 
supplied  with  10.3  KW  at  its  primary 

terminals,  and  its  efficiency  will  be  — — -  = 

lu.o 

97.09  per  cent.  Usually,  the  greater  part 
of  this  loss  of  300  watts  will  occur  at  all 
loads,  so  that  roughly  say  200  watts  will 
have  to  be  expended  in  operating  the 
transformer,  when  it  is  delivering  no 
power  to  its  secondary  circuit ;  i.  e.,  when 
its  secondary  circuit  is  open. 

We  have  seen  that  in  a  continuous-cur- 


THE  TRANSMISSION   OF  POWER.          253 

rent  circuit  the  activity  is  always  expressed 
as  the  product  of  the  amperes  and  the 
volts,  or  in  other  words,  on  the  rate  of  sup- 
ply of  current,  and  the  pressure  at  which 
that  current  is  supplied.  In  an  alternat- 
ing-current circuit,  however,  this  relation 
ceases,  as  a  general  rule,  to  be  strictly  ap- 
plicable. This  is  for  the  reason  that  the 
impulses,  or  waves  of  current,  do  not,  as  a 
rule,  exactly  coincide  with  the  impulses  or 
waves  of  E.  M.  F.  When  the  current 
waves  do  coincide,  or  keep  exactly  in  step 
with  the  E.  M.  F.  waves,  then  the  activity, 
in  watts,  is  the  product  of  the  amperes  and 
the  volts,  as  in  continuous-current  circuits, 
but  it  usually  happens  that  the  current 
waves  do  not  coincide,  or  are  out  of  step 
with,  the  E.  M.  F.  in  the  circuit,  and  gen- 
erally  lag  behind  the  latter.  If  we  could 
watch  the  waves  of  E.  M.  F.  and  current, 
we  should  find  that  the  crests  of  the  E.  M. 


254  THE   ELECTRIC   MOTOR   AND 

F.  waves  usually  arrived  ahead  of  the  cur- 
rent waves,  although  under  certain  circum- 
stances the  reverse  may  be  true,  and  the 
current  wave  crests  may  arrive  in  advance 
of  the  E.  M.  F.  wave  crests.  The  current 
in  these  cases  is  described  as  lagging  or 
leading  respectively. 

The  effect  of  a  lag  or  a  lead  is  to  pro- 
duce an  opposition  between  the  E.  M.  F. 
and  the  current  which  it  drives,  since  it  is 
evident,  that  during  the  entire  cycle,  the 
E.  M.  F.  will  not  be  in  the  same  direction 
as  the  current,  but  during  a  portion  of 
the  cycle,  the  current  and  the  E.  M.  F. 
waves  will  have  opposite  directions.  For 
this  reason  the  activity  of  the  E.  M.  F. 
will  not  be  so  great  as  the  product  of  the 
volts  and  the  amperes,  but  will  have  to  be 
reduced  by  a  factor  called  the  power  factor, 
always  less  than  unity,  and  only  reaching 


THE  TRANSMISSION   OF   POWER.          255 

unity  when  there  is  no  lag  or  lead  ;  i.  e., 
when  current  and  E.  M.  F.  waves  coincide. 
In  special  cases  the  power  factor  may  be 
as  low  as  say  1  per  cent.,  in  which  case 
the  current  and  the  pressure  would  be 
nearly  out  of  step,  the  crests  of  one  nearly 
coinciding  with  the  mean  levels  of  the 
other.  Under  ordinary  circumstances,  the 
power  factor  is  usually  more  than  50  per 
cent,  or  0.5,  and  it  is  quite  commonly  over 
90  per  cent,  or  0.9.  In  such  cases  we  have 
to  multiply  the  volts  by  the  amperes  and 
by  the  power  factor,  in  order  to  obtain  the 
true  activity.  In  other  words,  the  volts 
and  the  amperes,  when  multiplied  together, 
cannot  be  less  and  will  generally  be  more 
than  the  actual  activity  of  the  circuit  in 
which  they  are  measured. 

When  a  circuit  has  very  small  reactance, 
relatively    to    its    resistance,    the    power 


256  THE   ELECTRIC    MOTOR    AND 

factor  will  be  large,  or  nearly  100  per  cent. 
On  the  contrary,  when  the  reactance  is 
large  relatively  to  the  resistance,  the  power 
factor  will  be  small.  Consequently,  the 
power  factor  of  an  incandescent  lamp  is 
almost  exactly  100  per  cent.,  because  the 
filament,  having  only  a  single  bend  or  loop, 
possesses  an  extremely  small  reactance  and 
a  relatively  large  resistance.  Therefore,  if 
we  multiply  the  volts  and  the  amperes 
observed  at  the  terminals  of  an  incan- 
descent lamp,  or  group  of  incandescent 
lamps  supplied  on  an  alternating-cur- 
rent circuit,  we  obtain  almost  exactly  the 
real  activity  which  is  supplied  to  them. 
If,  however,  we  take  a  coil  of  wire  having 
a  large  number  of  turns  and  a  small 
resistance,  the  pressure  and  current,  ob- 
served at  the  terminals  of  this  coil,  may  be 
considerably  out  of  step,  or  may  be,  as  it 
is  frequently  called,  displaced  in  phase,  so 


THE  TRANSMISSION   OF  POWER. 


257 


that  the  product  of  the  volts  and  amperes 
may  be  considerably  in  excess  of  the  real 
activity  expended  in  the  coil. 


FIG.   62. — ALTERNATING-CURRENT  DYNAMO. 

Any  dynamo  for  generating  alternating 
E.  M.  F.'s  is  called  an  alternator.  Fig.  62, 
represents  an  alternator  employed  for 
electric  lighting.  Since  every  dynamo- 


258  THE  ELECTRIC   MOTOR   AND 

electric  generator  develops  in  its  armature 
E.  M.  F.'s  which  alternate,  it  is  evident  that 
a  continuous-current  machine  differs  from 
an  alternator  principally  in  the  fact  that  it 
employs  a  commutator  to  direct  all  the 
alternating-current  impulses  in  the  same 
direction,  so  far  as  the  external  circuit  is 
concerned.  In  Fig.  62,  is  shown  a  sexti- 
polar  machine,  driven  by  a  pulley  JP9  and 
provided  with  a  pair  of  collector  rings  r,  r, 
for  delivering  the  alternating  E.  M.  F.  to 
the  external  circuit.  The  machine  also 
drives  by  the  pulley  P^  a  small  continuous- 
cur  rent  generator  6r,  called  the  exciter,  the 
function  of  which  is  to  produce  a  suffi- 
ciently powerful  continuous  current  to 
excite  the  field-magnet  coils  J/,  M,  M,  of 
the  alternator. 

When  two  ordinary  alternators  are  con- 
nected by  a  pair  of  wires,  with  the  object 


PROPERTY  C 

THE  TRANSMISSION   O^JO^ER.         259 


of  employing  one  as  a  generated 
other  as  a  motor,  it  is  found  that  the  motor 
will  not  start  from  rest  when  connected  to 
the  running  generator.  This  is  for  the 
reason  that  before  the  armature  of  the 
motor  has  had  time  to  start  up  at  full 
speed  in  one  direction,  by  the  action  of 
any  particular  wave  of  current,  the  next 
and  opposite  wave  of  current  has  reversed 
the  electro-dynamic  force  and  arrested  the 
motion.  If,  however,  the  motor  armature 
be  brought,  by  an  externally  applied  force, 
up  to  the  speed  at  which  it  should  run  in 
order  to  develop  the  same  frequency  as  the 
generator,  then  if  its  field  magnets  are  ex- 
cited, its  armature  circuit  may  be  closed  in 
such  a  manner  that  the  armature  will  fall 
into  step  with  the  impulses  received  from 
the  generator,  and  the  motor  will  commence 
to  be  driven.  This  is  because  the  arma- 
ture of  the  motor  reverses  the  direction  of 


260  THE  ELECTRIC   MOTOR  AND 

its  C.  E.  M.  F.  nearly  in  synchronism  with 
the  reversal  of  the  direction  of  the  cur- 
rent. The  two  machines  then  keep  in 
step,  or  are  said  to  run  synchronously. 
The  motor  may  exert  a  powerful  torque 
and  exert  a  considerable  mechanical  activ- 
ity; but,  provided  that  it  be  not  too 
heavily  overloaded,  it  will  maintain  its 
synchronism  with  the  generator.  On 
being  subjected  to  an  excessive  load,  it  will 
fall  out  of  step,  will  fail  to  receive  activity 
from  the  generator,  and  will  then  rapidly 
come  to  rest. 

The  practical  difficulty  experienced  with 
alternating-current  motors,  until  recent 
times,  was  that  they  would  not  start  from 
rest,  so  that  a  prime  mover  of  some  kind 
was  necessary  in  order  to  bring  the  alter- 
nating-current motor  up  to  speed  before 
it  could  be  usefully  connected  with  the 


THE   TRANSMISSION   OF   POWER  261 

circuit.  Synchronous  alternating-current 
motors  of  this  type  have  been  brought 
up  to  speed  in  a  variety  of  ways.  In 
some  cases,  this  is  effected  by  means  of 
special  windings  on  the  armature,  capable 
of  acting  as  continuous-current  machines 
under  light  loads,  and  sometimes  by  storage 
batteries  and  auxiliary  motors.  In  other 
cases  continuous-current  exciters  are  em- 
ployed at  each  end  of  the  line,  as  ordi- 
nary continuous-current  generators  and 
motors,  thus  obtaining  sufficient  power 
from  the  line  circuit  from  the  generating 
exciter  to  the  motor  exciter,  to  be  able  to 
run  the  motor  armature  unloaded,  up  to 
synchronous  speed  when  the  exciters  would 
be  disconnected  from  the  circuit  and  the 
alternating-current  armatures  connected 
thereto.  The  inconvenience,  however,  of 
having  to  bring  the  motor  armature  up  to 
speed,  where  frequent  stoppages  are  neces- 


262  THE  ELECTRIC   MOTOR  AND 

sary,  becomes  so  great  that  the  synchro- 
nous alternating-current  motors  have  never 
come  into  extended  commercial  use.  A 
device,  however,  which  is  sometimes  used, 
is  to  provide  the  motor-armature  with  a 
double  winding,  one  winding  having  a 
commutator  for  the  production  of  con- 
tinuous currents,  and  the  other  winding 
arranged,  like  that  of  an  alternator  arma- 
ture, for  the  passage  of  alternating  currents. 
By  connecting  the  continuous-current 
winding  with  the  alternating-current 
mains,  the  motor  may  be  started  and 
brought  up  to  speed  by  allowing  the  field 
magnets  to  reverse  their  polarity  at  each 
alternation  of  the  current,  so  that  the 
magnetic  flux  reverses  coincidently  in  both 
field  and  armature  at  every  alternation 
of  current.  After  full  speed  has  been 
attained,  the  alternating-current  winding 
is  connected  to  the  circuit,  so  that  the 


THE  TRANSMISSION   OF   POWER.          263 

motor  runs  synchronously,  while  the  con- 
tinuous-current winding  supplies  the  cur- 
rent necessary  to  steadily  energize  the  field 
magnets. 

The  difficulty  of  starting  and  operating 
synchronous  alternating-current  motors, 
has,  however,  led  to  the  introduction  and 
development  of  multiphase  alternating- 
currents  and  multiphase  motors. 

A  multiphase  alternating-current  system 
is  a  system  of  two  or  more  circuits  tra- 
versed by  independent  alternating  currents, 
possessing  a  definite  difference  of  phase. 

A  diphase  system,  or  two-phase  system, 
is  a  system  consisting  of  circuits  having 
two  alternating  currents  differing  in  phase 
by  one  quarter  of  a  cycle. 

A  triphase  system,  or  three-phase  system, 
is  a  system  of  circuits  having  three  alter- 


264  THE    ELECTRIC    MOTOR   AND 

nating  currents,  differing  in  phase  by  one- 
third  of  a  cycle. 

Multiphase  systems  of  any  complexity 
may  exist,  but  in  practice  not  more  than 
three  separate  currents  are  employed. 


B 
b 


FIG.  63. — DIAGRAM  OF  DIPIIASE  SYSTEM  WITH  FOUR 
CONDUCTORS. 

Fig.  63,  represents  the  simplest  form  of 
diphase  system,  comprising  two  distinct 
circuits  supplied  with  alternating  currents 
from  a  common  source  at  A.  The  circuit 
ab,  cd,  taken  by  itself  is  a  simple  alter- 
nating-current circuit.  The  circuit  ef,  gh, 
taken  similarly  is  also  a  simple  alternat- 
ing-current circuit,  but  these  circuits,  taken 


THE  TRANSMISSION    OF   POWER.          265 

together,  constitute  a  dipJiase  system,  for 
the  reason  that  the  waves  of  E.  M.  F. 
and  current  generated  in  the  circuit  abed, 
differ  in  phase  by  one  quarter  of  a  cycle 
from  those  generated  in  the  circuit  efgli. 
The  impulses  reach  their  crests  in  one 
circuit,  when  at  their  zero  or  mean  levels 
in  the  neighboring  circuit.  This  result 
may  be  obtained  by  employing  either  two 
ordinary  or  Uniphase  generators,  rigidly 
coupled  together  on  the  same  shaft,  in 
such  a  position  that  the  E.  M.  F.  waves 
in  one  are  generated  one  quarter  cycle 
ahead  of  the  E.  M.  F.  waves  in  the  other ; 
or,  by  employing  two  windings  on  the 
armature  of  one  alternator  so  arranged  as 
to  produce  the  necessary  difference  in 
phase. 

Instead  of  employing  two  entirely  sepa- 
rate circuits  for  the  two  alternating   cur- 


266 


THE   ELECTRIC    MOTOR   AND 


rents  of  a  diphased  system,  as  shown  in 
Fig.  63,  a  common  return  conductor  may 
be  employed  and  only  three  wires  used  as 
in  Fig.  64.  In  such  cases,  the  third,  or 
middle  conductor,  is  made  about  40  per  cent. 


B 
b 


FIG.  64.— DIAGRAM   OF   DIPHASE  SYSTEM  WITH  THREE 
CONDUCTORS. 


heavier  in  order  to  carry  the  increased  cur- 
rent strength.  The  diphase  system  requires 
that  the  waves  of  current  and  E.  M.  F.  in 
the  conductors  a  b  d,  shall  be  a  quarter 
cycle  out  of  step  with  those  in  the  con- 
ductor g  h  d. 


THE  TRANSMISSION   OF   POWEK.          267 

A  triphaser  is  an  alternator  which  pro- 
duces three  E.  M.  Fs.  differing  from  one 
another  in  phase  by  one  third  of  a  cycle. 
Such  triphase  currents  might  be  produced 
by  three  Uniphase  armatures  rigidly 


a 

b 


hi2 


E 


FIG.  65. — TRIPHASE  Six- WIRE  SYSTEM. 

clamped  together  on  a  single  shaft,  but  so 
set  that  the  E.  M.  Fs.  differ  in  phase  by 
one  third  of  a  complete  cycle.  Such  a  com- 
bination is  diagranimatically  represented 
in  Fig.  65,  where  the  three  separate  circuits 
have  Uniphase  currents,  but  the  current 
waves  in  the  three  circuits  differ  by  one 


268  THE  ELECTRIC   MOTOR  AND 

third  of  a  cycle.  In  practice,  however,  six 
wires  are  never  used  for  a  triphaser,  but 
three  wires  only,  each  wire  serving  in  turn 
as  the  return  of  the  other  two.  This  ar- 
rangement is  represented  in  Fig.  66. 


o 

1 

f! 

1 

D 

i 

3    B 

r 

Jcl 

E 

j 

3 

ft* 

FIG.  66. — TRIPHASE  THREE- WIRE  SYSTEM. 

Fig.  67,  shows  a  form  of  triphaser  having 
40  poles  and  capable  of  maintaining  an 
activity  of  500  KW;  166  2/3  KW  in  each 
of  its  three  circuits.  The  pressure  is  500 
volts  between  each  pair  of  terminals.  The 
armature  is  driven  at  108  revolutions  per 
minute.  The  frequency  is  36 ~  per  sec- 
ond. The  dimensions  of  this  machine  are 


THE  TRANSMISSION   OF   POWER.          269 


FIG.  67.— THREE-PHASE  ALTERNATOR,  40  POLES,  500  KW, 


270  THE   ELECTRIC   MOTOR. 

107"  x  213"  and  its  height  150".  The 
total  weight  is  108,000  pounds,  or  about 
216  pounds  per  KW  of  output.  The 
armature  has  three  separate  windings  in 
which  tri phase  E.  M.  Fs.  are  developed. 
The  three  main  leads  are  shown  in  the 
figure. 

Fig.  68,  shows  another  form  of  belt- 
driven  triphaser,  having  10  poles  and  mak- 
ing 600  revolutions  per  minute.  The 
frequency  is  50  ~  per  second,  the  activity 
250  KW;  or,  83  1/3  KW,  in  each  cir- 
cuit. This  machine  is  seen  to  be  sepa- 
rately excited.  Its  weight  is  about  30,000 
pounds,  or  120  pounds  per  KW. 

Another  type  of  multiphase  system  is 
the  monocydic  system.  This  system  has 
been  designed  for  use  in  central  stations 
where  the  main  load  is  that  of  lighting, 


272  THE   ELECTRIC   MOTOR   AND 

but  where  alternating-current  motors  re- 
quire to  be  operated  from  the  circuit.  The 
armature  is  wound  with  two  sets  of  coils, 
one  constituting  the  main  winding,  which 
corresponds  to  that  of  an  ordinary  uni- 
phaser,  while  the  second  winding  is  of 
smaller  cross-section  and  fewer  turns,  and 
is  connected  to  the  centre  of  the  main 
winding  as  shown  in  Fig.  69,  at  A,  where 
a  o  b,  represents  the  main  armature  wind- 
ing, and  o  c,  the  short  coil  or  teaser  winding. 
Three  terminals  are  thus  led  out  from  the 
the  armature  at  a,  b  and  c.  The  terminals 
a  and  J,  connected  by  means  of  collector 
rings  and  brushes  to  the  external  circuit, 
constitute  the  lighting  circuit,  while  a 
third  wire  from  <?,  enables  an  alternating- 
current  motor  to  be  operated  in  conjunction 
with  the  other  two.  The  windings  are  so 
arranged  that  the  E.  M.  F.  in  C  I),  is  in 
diphase  relation  to  that  in  A  B,  as  rep- 


m.          •  J 

resented  diagrammaticallyNtt;'®,  jn  Fig. 
69,  the  loop  a  o  b,  being  woiilid  on  the 
drum  at  right  angles  to  the  half  loop  o  c. 


FIG.  69. — DIAGRAMS  OF  MONOCYCLIC  ARMATURE  WINDING. 

A  inonocydw  armature  is  represented  in 
Fig.  70.     A,  B  and   C\  are  the  three  col- 


FIG.  70. — MONOCYCLIC  ARMATURE. 

lector   rings,  forming  the   main  terminals 
of  the  armature.     The  windings  are  just 


274  THE  ELECTRIC   MOTOK  AND 

visible  in  the  slots  left  between  the  teeth 
or  iron  armature  projections.  The  shape 
of  the  coils  is  represented  in  Fig.  71.  The 
main  coils  are  flat,  while  the  teaser  coils 


FIG.  71.— MAIN  AND  TEASER  COILS. 

are  bent  in  such  a  manner  as  to  permit 
them  to  be  laid  across  the  main  coils  in  a 
midway  position,  so  as  to  generate  their 
E.  M.  Fs.  a  quarter  cycle  out  of  step  with 
those  in  the  main  coils. 


THE  TRANSMISSION   OF   POWER.          275 

A  form  of  'monocyclic  alternator  is  rep- 
resented in  Fig.  72.     This  is  a  120  KW 


FIG.  72. — MONOCYCLIC  ALTERNATOR,  40  POLES,  120  KW. 

machine,  wound  for  60 ~  per  second,  and 
a  pressure  of  1,1 50,  2,300  or  3,450  volts 
between  the  main  terminals,  according  to 


276  THE   ELECTRIC   MOTOR. 

requirements.     This  machine  weighs  about 
15,000  pounds  or  125  pounds  per  KW. 

The  connections  for  use  with  a  mono- 
cyclic  system  are  shown  in  Fig.  73.  Here 
the  generator  terminals  A  and  J3,  are  con- 
nected with  the  mains  for  lighting.  T^ 
represents  a  step-down  transformer  whose 
primary  terminals  P^  and  P^  are  con- 
nected to  the  mains  A  and  B,  respec- 
tively, at  a  pressure,  of  say  2,200  volts. 
The  secondary  terminals  siy  s2  and  s3,  of 
this  transformer  constitute  a  Uniphase 
three-wire  system,  having  220  volts  be- 
tween Si  or  .<?3  or  110  volts  between  s^  and 
S2;  and  110  volts  between  s2  and  s3,  with- 
out any  difference  in  phase.  This  is  ob- 
tained by  dividing  the  secondary  coil  into 
halves.  The  secondary  circuit  is  connected 
with  lamps  on  each  side  of  the  three-wire 
system  as  shown.  T±,  is  a  step-down  trans- 


278  THE   ELECTRIC   MOTOR   AND 

former,  transforming  from  2,200  to  say, 
50  volts,  for  operating  two  arc  lamps  in 
parallel.  The  primary  terminals  of  this 
transformer  are  connected  to  the  main 
leads  A  and  B.  rl\,  is  a  transformer 
whose  primary  terminals  are  also  con- 
nected with  A  and  B,  while  the  sec- 
ondary coil  in  this  case,  having  a  single 
pair  of  terminals,  is  connected  directly 
with  incandescent  lamps,  and  also  with 
a  small  fan  motor,  which  being  of  small 
size  can  be  operated  without  the  use  of 
multiphase  currents.  T6,  is  also  a  uni- 
phase  transformer  connected  with  the  pri- 
mary mains  A.  and  B,  and  feeding  in  its 
secondary  circuit  110- volt  lamps,  as  well  as 
two  arc  lamps  through  a  compensator. 

Hitherto  we  have  simply  examined  the 
devices  which  have  been  operated  from 
the  mains  A  and  B,  without  the  use  of 


THE  TRANSMISSION   OF   POWER.          279 

the  poiver  wire,  the  dotted  line  connected 
with  the  terminal  C,  and  all  that  we  have 
yet  examined  might  have  been  obtained 
from  an  ordinary  uniphaser.  To  operate 
an  induction  motor,  two  transformers  have 
to  be  employed,  such  as  2\  and  T2,  the 
primary  terminals  of  one  being  connected 
between  A  and  C,  and  those  of  the  other 
between  B  and  C.  The  secondary  termi- 
nals, when  connected  with  the  motor,  as 
shown,  generate  a  system  of  triphase  cur- 
rents in  the  motor  a.  Similarly,  the  two 
transformers  T7  and  T8,  one  connected 
with  its  primary  terminals  between  A  and 
B,  and  the  other  transformer  connected 
with  its  terminals  between  O,  and  the 
centre  of  the  primary  in  T8,  produce  in 
their  secondary  circuits  a  system  of  tri- 
phase E.  M.  Fs.  and  currents,  capable  of 
operating  the  induction  motor  as  well  as 
the  incandescent  lamps. 


280  THE   ELECTRIC    MOTOR   AND 

A  monocyder,  therefore,  produces  a  uni- 
phase  main  E.  M.  F.  in  its  main  circuit, 
which  is  employed  for  all  uniphase  pur- 
poses, such  as  lighting,  or  for  the  operation 
of  synchronous  motors.  It  also  generates 
in  a  subsidiary,  or  auxiliary  coil,  an 
E.  M.  F.  in  diphase  relation  with  the  main 
E.  M.  F.  and,  by  combining  these  two 
diphase  E.  M.  Fs.  through  the  connec- 
tion of  the  third  wire,  triphase  E.  M.  Fs. 
can  be  produced  in  the  secondary  circuits 
of  suitably  connected  transformers. 

Fig.  74,  shows  the  connections  employed 
for  the  distributing  circuit  of  a  triphaser. 
Here  any  pair  of  conductors  may  be  re- 
garded as  an  independent  uniphase  circuit, 
from  which  step-down  transformers  for 
uniphase  work  may  be  operated.  Thus 
TI,  T2  and  T3  are  step-down  transformers, 
each  connected  with  one  pair  of  high-pres- 


THE   TRANSMISSION   OF   POWER. 


281 


sure  wires.  A  pair  of  transformers,  how- 
ever, operated  from  any  two  of  the  three, 
as  shown  at  ^  and  £3,  will  produce  in  their 
secondary  circuits,  when  united  in  the 
manner  represented,  a  triphase  system  of 


FIG.  74. — CONNECTIONS  OF  TRIPHASE  SYSTEM. 

E.  M.  Fs.  and  currents  suitable  for  operat- 
ing a  triphase  alternating-current  motor 
MI,  but  three  transformers  may  also  be 
employed,  each  connected  across  a  pair  of 
high-pressure  wires  as  shown  at  ta,  t±  and 
ts.  Their  secondary  circuits  are  connected 


282 


THE   ELECTRIC   MOTOR  AND 


with  the  three  terminals  of  the  triphase 
induction  motor  M. 


Fig.  75,  similarly  represents  the  connec- 
tions of  a  diphaser.     Here   two  independ 


FIG.  75. — CONNECTIONS  OF  DIPHASE  SYSTEM. 

ent  circuits  are  shown,  each  of  which  may 
be  treated  as  a  uniphase  circuit,  as  seen 
at  T^  and  T2.  By  operating  two  trans- 
formers, one  from  each  circuit  and  connec- 
ting their  secondaries  together,  as  shown 
at  ^  and  t2,  a  diphase  system  of  E.  M.  Fs. 


THE   TRANSMISSION   OF   POWER.          283 

and  currents  may  be  obtained,  capable  of 
operating  a  diphase  motor  M.  As  already 
pointed  out  three  wires  are  theoretically 
sufficient  for  the  operation  of  this  system. 

The  triphase  system  of  three  wires  pos- 
sesses a  distinct  saving  in  copper  over  an 
ordinary  Uniphase,  or  a  diphase  system, 
for  a  given  maximum  pressure  between 
any  pair  of  conductors  and  a  given  per- 
centage of  drop  in  the  lines.  The  saving 
in  copper  amounts  to  25  per  cent,  of  that 
required  for  a  four- wire  diphase,  or  a  two- 
wire  Uniphase  system. 


CHAPTER  X. 

ROTATING    MAGNETIC    FIELDS. 

IT  now  remains  to  explain  the  manner 
in  which  a  multiphase  alternating-current 
motor  operates  when  its  stationary,  or 
stator  coils,  are  traversed  by  multiphase 
currents. 

Let  us  suppose  that  a  field  frame  is  ar- 
ranged with  four  poles  and  four  coils,  as 
shown  in  Fig.  76.  Let  coils  1  and  3,  be 
joined  together  in  series  in  one  circuit,  and 
coils  2  and  4,  be  also  joined  together  in 
series  in  another  circuit ;  moreover,  let 
these  two  circuits  be  connected  to  the  two 
windings  of  a  diphaser ;  then,  when  one 
circuit  has  its  full  current  strength,  the 


284 


THE   TRANSMISSION    OF   POWER.          285 

other  circuit  will  have  no  current  passing 
through  it.  Let  us  suppose  that  at  the  in- 
terval of  time  represented  at  A,  Fig.  76, 


FIG.  76.— DIAGRAM  ILLUSTRATING  A  ROTATING  MAG- 
NETIC FIELD. 

coils  1  and  3,  are  receiving  a  wave  of  cur- 
rent which  produces  a  north  pole  at  1,  and 
a  south  pole  at  3.  At  this  instant  there 
will  be  no  current  in  the  coils  2  and  4.  A 


286  THE   ELECTRIC    MOTOR   AND 

small  compass  needle,  pivoted  at  the  centre 
of  the  field  frame,  would,  therefore,  point 
to  pole  3. 

Next  suppose,  that  a  quarter  cycle 
elapses,  as  at  B  /  then  the  current  in  the 
coils  1  and  3,  will  have  disappeared,  and 
the  current  in  2  and  4,  will  have  attained 
its  maximum  strength.  Under  these  con- 
ditions, a  north  pole  will  be  developed  at 
4,  and  a  south  pole  at  2,  so  that  the  com- 
pass needle  will  have  to  rotate  through 
90°,  and  will  now  point  to  2.  Again,  at 
the  next  quarter  cycle  represented  at  (7, 
the  current  in  2  and  4,  will  have  died 
away,  but  the  current  in  1  and  3,  will 
have  the  opposite  direction  to  that  at  A  ; 
that  is  to  say,  if  A,  represents  the  effect  of 
the  positive  wave  (7,  represents  the  effect 
of  the  negative  wave.  A  north  pole  will, 
therefore,  be  formed  at  3,  and  a  south  pole 


THE  TRANSMISSION   OP  POWER.         287 

at  1 .  The  compass  needle  will,  therefore 
be  rotated  to  1,  having  described  180°. 
Again,  Z>,  represents  the  condition  at  the 
next  quarter  cycle,  when  the  current  flows 
through  2  and  4,  producing  a  north  pole 
at  2,  and  a  south  pole  at  4.  The  needle 
will  now  be  pointing  to  4,  and  will  have 
rotated  through  270°.  Finally,  after  a 
complete  cycle  has  elapsed  the  condition 
at  A,  will  be  reproduced,  when  the  needle 
will  have  completed  a  revolution.  It  is 
evident  that  the  effect  of  the  diphase  cur- 
rents in  the  field  frame  has  been  to  pro- 
duce a  rotation  of  the  magnetism  of  the 
field,  in  obedience  to  which  the  compass 
needle  rotates  once  to  each  complete  cycle. 

If  the  frequency  in  the  circuits  be,  say 
50  cycles  per  second,  the  compass  needle 
may  be  expected  to  make  50  complete 
revolutions  per  second,  and  would  consti- 


288  THE   ELECTRIC   MOTOR   AND 

tute  a  diminutive  moving  part  or  rotor. 
We  have  explained  the  successive  steps  of 
this  rotating  field  that  occur  in  Fig.  76,  on 
the  supposition  that  they  take  place  in 
positions  90°  apart.  In  practice,  however, 
motors  are  frequently  so  constructed  that 
the  magnetic  field  rotates  almost  uniformly 
around  the  frame,  instead  of  by  jumps. 

The  motor  constituted  by  the  field  frame 
and  the  rotating  compass  needle  would  ob- 
viously be  very  feeble.  Magnetic  action, 
however,  may  be  intensified  in  various 
ways,  either  by  employing  a  larger  or  more 
powerful  compass  needle,  such,  for  ex- 
ample, as  a  suitably  pivoted  electromagnet, 
or,  by  employing  a  mass  of  iron  for  the 
rotating  part,  wound  with  coils  of  wire 
forming  closed  circuits,  so  that  the  moving 
or  rotating  magnetic  field  may  induce  in 
these  coils  powerful  currents,  whose  mag- 


THE  TRANSMISSION   OF   POWER.          289 

netic  flux  will  be  attracted  by  the  rotating 
field,  thus  turning  the  armature  around. 

There  are  thus  two  classes  of  multiphase 
motors,  both  of  which  employ  a  rotating 
field.  In  one  class  the  rotating  field  acts 
upon  a  magnetized  armature,  which,  after 
being  set  in  rotation,  keeps  in  step  or  in 
synchronism  with  the  rotating  field.  In 
the  other  class,  the  rotating  field  acts  so  as 
to  induce  currents  in  the  armature  by  the 
difference  of  speed  between  the  rotating 
field  and  the  rotating  armature,  so  that  the 
armature  never  quite  attains  the  speed  of 
the  field,  and  lags  behind  it  by  an  amount 
sometimes  called  the  slip,  which  depends 
upon  the  torque  or  load.  The  first  class 
embraces  what  are  called  synchronous  mul- 
tiphase motors  ;  the  second  class,  are  called 
induction  multiphase  motors,  or  simply 
induction  motors. 


290  THE   ELECTRIC   MOTOR  AND 

There  is  a  marked  difference  between 
synchronous  multiphase  motors  and  syn- 
chronous Uniphase  motors.  The  latter  are 
incapable  of  starting  under  ordinary  practi- 
cal conditions,  since  the  magnetic  field  pro- 
duced by  a  Uniphase  current  does  not 
rotate,  but  merely  oscillates  to-and-fro. 
The  former  are  so  designed  as  to  be  capa- 
ble of  self-starting,  owing  to  the  influence 
of  the  rotating  magnetic  field,  which  pulls 
the  armature  around  with  it.  If  one  of 
the  diphase  circuits  of  the  field  frame  be  re- 
versed it  will  be  found  that  the  effect  is  to 
reverse  the  direction  of  rotation  of  the  field 
and,  therefore,  the  direction  of  rotation  of 
the  armature. 

Fig.  77  represents  diagram rnatically  the 
action  of  a  triphase  rotating  field.  Here 
six  poles  1,  2,  3,  4,  5  and  6,  are  represented, 
with  their  coils  so  arranged  that  1  and  4,  are 


THE   TRANSMISSION 


in  series  in  one  circuit,  and u  2  and  5,  i$fsoO,  ^ 
series  in  the  second  circuit,  and  3  and  6,  in 
series  in  the  third  circuit.     Six  conditions 


&  DIESEL  £/,'; 


PROPERTY  ( 

291 


FIG.  77. — DIAGRAM  OP  TRIPHASE  ROTATING  FIELD. 

are  represented  at  A,  B,  C,  D,  E,  and  F, 
during  successive  sixths  of  one  complete 
cycle.  At  A,  the  compass  needle  is  shown 


292  THE  ELECTRIC   MOTOR   AND 

pointing  to  pole  1,  the  current  being  a 
maximum  in  coils  1  and  4.  At  B,  the 
needle  is  shifted  to  pole  6,  the  current 
being  now  a  maximum  in  coils  3  and  6. 
Similarly,  at  each  successive  sixth  of  a 
period,  the  needle  will  have  shifted  around 
one-sixth  of  the  revolution  as  the  current 
successively  rises  and  falls  in  different  cir- 
cuits. It  will  be  seen  that  the  difference 
between  a  diphase  field  frame,  and  a 
triphase  field  frame,  consists  in  the  number 
and  arrangement  of  the  coils,  but  that  the 
effect  is  otherwise  the  same,  the  result  of 
combining  the  effects  of  successive  current 
waves  being  to  produce  a  rotary  magnet- 
ism. The  armature,  as  before,  may  be  of 
the  synchronous,  or  of  the  induction  type. 
It  will  be  readily  understood  that  Fig.  7V 
is  diagrammatic  only.  The  actual  rotation 
of  the  field  being  usually  obtained  by  a 
somewhat  different  winding. 


THE  TRANSMISSION   OF   POWER.          293 

A  synchronous  multiphase  motor  has 
the  same  speed  at  all  loads.  If  overloaded 
it  will  come  to  rest,  but  will  start  again 
from  rest  when  the  load  is  removed.  An 
induction  motor  will  very  nearly  reach  the 
full  rotary  speed  of  the  field  at  light  load, 
but  will  be  retarded,  or  will  slip,  as  already 
mentioned,  at  full  load.  The  amount  of 
slip  is  comparatively  small,  being  only 
about  3  per  cent,  in  large  motors,  and 
about  5  per  cent,  in  small  motors.  Induc- 
tion motors  may  be  designed  which  will 
start  from  rest  under  a  very  powerful 
torque.  It  is  usually  necessary,  especially 
with  large  motors,  to  insert  resistances  into 
the  armature  circuit  at  starting,  in  order  to 
check  the  very  powerful  currents  which 
tend  to  be  developed  in  them  when  started 
from  rest ;  for,  since  the  E.  M.  Fs.  induced 
in  the  armature  are  proportional  to  the 
difference  in  speed  between  the  armature 


294  THE   ELECTRIC    MOTOR   AND 

and  the  rotary  field,  it  is  evident  that  when 
just  starting  this  difference  of  speed  will 
be  a  maximum,  and  the  current  will 
be  very  powerful,  producing  reactionary 
effects  that  are  disadvantageous.  The 
effect  of  inserting  resistance  in  the  arma- 
ture circuit  is  to  check  the  strength  of 
these  currents  and  so  improve  the  starting 
torque  of  the  motor. 

A  form  of  tri phase  motor,  of  15-horse- 
power  capacity,  is  represented  in  Fig.  78. 
The  three  main  terminals  are  seen  at  A,  B, 
and  C.  The  field  frame  F,  is  of  laminated 
iron.  W,  is  a  portion  of  the  field  winding. 
The  lever  Z,  is  provided  for  the  purpose  of 
starting  the  motor  effectively.  When  the 
lever  is  in  the  position  shown,  resistances 
are  left  in  the  armature  circuit  as  above 
described,  so  as  to  obtain,  when  starting,  a 
more  powerful  and  less  wasteful  torque, 


THE   TRANSMISSION    OF   POWER. 


295 


and  a  reduced  current  in  the  armature 
coils,  which  are  hidden  from  view.  As 
soon  as  the  armature  has  come  up  to  speed, 


FIG.  78. — MULTIPHASE  INDUCTION  MOTOR. 

the  lever  Z,  is  pushed  in  toward  the  arma- 
ture, thereby  bringing  a  metal  collar  into 
contact  with  the  strips  S,  thus  short-circuit- 
ing the  resistance,  and  improving  the  action 
of  the  motor  for  full  speed.  In  order  to 


296 


THE   ELECT RfC   MOTOR   AND 


reverse   the   direction   of    motion    of   the 
armature,  it  is  sufficient  to  reverse  any  pair 


FIG.  79. — HOIST,  WITH  10  KILOWATT  MULTIPHASE  MOTOR. 

of  wires  on  the  terminals  A,  B  and  G. 
This  has  the  effect  of  reversing  the  direc- 
tion of  the  rotating  field.  By  examining 


THE  TRANSMISSION   OF   POWER.          297 

the  figure,  it  will  be  seen  that  the  dimen- 
sions of  this  motor  are  relatively  very 
small  as  indicated  by  the  foot  rule  that  lies 
extended  at  its  base. 

In  Fig.  79,  a  10  KW  triphase  motor  M, 
is  shown,  connected  to  a  hoist.  Here  F,  is 
the  field  winding,  and  A,  the  winding  on 
the  rotating  armature. 

A  marked  advantage  possessed  by  mul- 
tiphase motors,  either  of  the  diphase  or 
triphase  type,  lies  in  their  simplicity. 
They  require  no  commutator,  and  their 
winding  is  of  a  very  simple  descrip- 
tion. They  are  compact  and  require  the 
minimum  amount  of  attention.  These 
facts,  taken  in  connection  with  the  facility 
of  transforming  alternating-current  pres- 
sures, have  given  a  great  impetus  to  the 
manufacture  and  use  of  multiphase  motors. 


THE   TRANSMISSION   OF   POWEK.  299 

Fig.  80  shows  a  form  of  tripliase  motor 
suitable  for  driving  line  shafting.  It  is 
secured  in  an  inverted  position  to  a  ceiling 
or  elevated  beam. 

The  multiphase  motor  is  sometimes  used 
as  a  starter  for  a  large  Uniphase  syn- 
chronous motor.  Fig.  81  represents  such 
an  arrangement.  Here  the  diphase  motor 
M,  is  capable  of  being  moved  forward  on 
its  base  by  the  wheel  H,  so  that  its  pulley 
§,  engages  by  friction  with  the  pulley  R,  of 
the  large  synchronous  motor  S.  This  is 
done  in  order  to  bring  the  large  synchronous 
motor  up  to,  or  slightly  in  excess  of,  its  syn- 
chronizing speed.  As  soon  as  this  speed 
has  been  attained,  the  circuit  of  the  uni- 
phase  motor  is  closed,  enabling  it  to  be 
operated  from  that  circuit  and  to  absorb 
energy  from  the  generator  at  the  transmit- 
ting end  of  the  line.  The  friction  clutch  (7, 


THE   TRANSMISSION   OF   POWEK.  301 

is  then  operated  to  connect  the  pulley  P, 
and  its  load  with  the  synchronous  motor, 
which  torque  can  now  be  taken  by  the 
motor  without  its  falling  out  of  synchron- 
ism. The  diphase  motor  M,  is  then  with- 
drawn and  stopped. 


CHAPTER  XL 

ALTERNATING-CURRENT   TRANSMISSIONS. 

As  we  have  already  pointed  out, 
economy  in  electric  transmission  necessi- 
tates the  use  of  high  pressure  in  the  line 
when  the  distance  between  generating  and 
receiving  station  is  great,  and  that  con- 
siderable practical  difficulty  exists  in 
obtaining  continuous-current  translating 
devices  which  may  be  operated  by  it. 

The  use  of  alternating  currents  for  the 
transmission  of  power  obviates  the  diffi- 
culty as  regards  high-pressure  translating 
devices,  since  by  means  of  the  alternat- 
ing-current transformer,  the  high  pressure 


THE  TRANSMISSION   OF  POWER.         303 

on  the  line  can  readily  be  transformed  at 
the  generator  and  motor  to  any  desired 
low  pressure. 

Alternating-current  systems  of  transmis- 
sion may  be  classified  as  Uniphase  or  multi- 
phase. The  use  of  any  uniphase  power 
system  is  open,  however,  to  the  objection 
that,  as  yet,  no  electric  motor  of  any  con- 
siderable size  has  been  designed,  which 
will  start  from  rest  when  directly  con- 
nected with  such  circuit.  For  this  reason 
the  tendency  of  recent  engineering  prac- 
tice has  been  towards  multiphase  trans- 
mission systems. 

In  order  to  compare  the  relative  advan- 
tages of  economy  between  uniphase  and 
multiphase  systems,  so  far  as  relates  to  the 
weight  of  the  conductors  employed,  some 
common  criterion  must  be  adopted  as 


304  THE   ELECTRIC   MOTOR   AND 

a  basis  of  comparison.  It  is  obvious,  if  a 
given  weight  of  copper  be  employed  in  a 
Uniphase  system  of  transmission,  at  a  pres- 
sure of  say  4,000  volts,  that  it  would  be 
possible  to  reduce  this  weight  of  copper 
either  on  a  uniphase  or  a  multiphase  system 
by  employing  a  higher  pressure.  Conse- 
quently, the  basis  of  comparison  must  be  a 
given  maximum  effective  pressure.  This 
maximum  permissible  pressure  might  be 
measured  between  any  wire  in  the  system 
and  the  ground,  or,  between  any  pair  of 
conductors  independently  of  the  ground. 
The  latter  is  usually  the  basis  of  compari- 
son, since,  when  circuit  wires  are  buried 
side  by  side  in  a  conduit,  or  are  suspended 
side  by  side  from  poles,  it  is  the  insulation 
between  these  wires  which  determines  the 
electric  security  of  the  system  and  this  in- 
sulation is  not  from  a  practical  standpoint 
to  be  regarded  as  the  mere  number  of  ohms, 


THE   TRANSMISSION   OF   POWER.          305 

or  megohms,  existing  between  the  con- 
ductors, but  in  their  latent  capability  of 
maintaining  this  degree  of  insulation  under 
all  normal  circumstances. 

Let  us  suppose  that  the  maximum  per- 
missible pressure  between  any  pair  of  wires 


FIG.  82. — UNIPHASE  CIRCUIT. 

is  fixed  at  10,000  volts  effective,  as  indicated 
by  a  voltmeter  connected  between  them; 
then  the  uniphase  system  would  have 
10,000  volts  between  its  single  pair  of 
wires,  as  shown  in  Fig.  82,  where  G,  is  the 
generator,  My  the  motor  and  1  1  and  2  2,  the 
wires.  A  four-wire  diphase  system  would 
have  10,000  volts  between  the  wires  of  each 
circuit,  as  shown  in  Fig.  83.  The  three- 


306  THE   ELECTRIC   MOTOR   AND 

wire    diphase    system  would  have    10,000 
volts  between  the  outside  wires  and  7,070 


5 

f 

1 

< 

A 

i 

Q,| 

1 

4 

§2 

V 

2l 

4  4 

FIG.  83. —FOUR- WIRE  DIPHASE  CIRCUIT. 

volts  between  neighboring  wires,  as  shown 
in  Fig.  84,  and  a  triphase  system   would 


3  3 

FIG.  84.— THREE-WIRE  DIPHASE  SYSTEM. 

have  10,000  volts  between  any  two  of  the 
three  wires,  as  shown  in  Fig.  85.     Under 


THE   TRANSMISSION   OF   POWER.          307 

these  conditions  the  Uniphase,  and  the  in- 
dependent-circuit dipkase  or,  the  four-wire 
dipkase,  possess  the  same  relative  economy 
in  conductors.  The  triphase  system,  how- 
ever, requires  25  per  cent,  less  copper, 
altogether,  than  either  the  uniphase,  or  the 


FIG.  85. — TRIPHASE  SYSTEM. 

independent-circuit  diphase,  while  the  inter- 
linked,  or  three-wire  dipliase,  requires  45  per 
cent,  more  copper  than  the  uniphase,  on 
the  basis  of  Fig.  84,  since  when  the  maxi- 
mum effective  pressure  is  reached  between 
wires  1  and  3,  the  working  pressure  is  only 
7,070  volts.  If  the  pressure  between  out- 
side conductors  could  be  neglected,  and 


308  THE  ELECTRIC   MOTOR  AND 

10,000  volts  retained  between  working 
wires,  then  the  three-wire  diphase  would 
save  27  per  cent,  in  copper  over  either  the 
uniphase,  or  the  four-wire  diphase,  and 


FIG.  86. — STAR  CONNECTION. 

thus  slightly  exceed  the  triphase   system 
in  economy. 

There  are  two  methods  of  connecting 
the  circuits  of  a  triphase  system;  namely, 
the  star  method,  and  the  triangle  method. 


THE   TRANSMISSION    OF   POWER.  309 

These  are  illustrated  in  Figs.  86  and  87, 
respectively.  Both  methods  have  been 
used.  The  E.  M.  Fs.  in  each  branch  differ 
in  phase  by  l/3rd  cycle,  in  each  case. 


D  E 

FIG.  87.— TRIANGLE  OR  DELTA  CONNECTION. 

The  connections  employed  for  step-up 
and  step-down  transformers,  at  each  end  of 
a  transmission  line,  are  outlined  in  Figs.  88 
and  89,  where  Fig.  88  indicates  a  uniphase 
and  Fig.  89  the  triphase  system.  Here  the 
pressure  generated  by  the  alternator  and 


310 


THE   ELECTRIC    MOTOR  AND 


motor  may  be,  say  1,000  volts,  while  tliat 
on   the   line   may    be    10,000    volts.     Ob- 


FIG.  88. — STEP-UP   AND    STEP-DOWN    TRANSFORMERS 
WITH  UNIPHASE  SYSTEM. 

viously,  however,  the  pressure  between  the 
line  terminals,  at  the  step-up  transformer, 


FIG.  89.— STEP-UP  AND  STEP-DOWN  TRANSFORMERS  OF 
TRIPHASE  TRANSMISSION  SYSTEM. 


will  be  greater  than  the  pressure  at  the  line 
terminals  at  the  receiving  end,  owing  to 
the  drop  in  the  line. 


THE  TRANSMISSION   OF   POWER.          311 

No  better  illustration  can  be  given  of 
methods  of  alternating-current  power  trans- 
mission than  that  afforded  by  the  system 
now  in  operation  at  Niagara  Falls.  Here 
energy,  taken  by  turbines  from  water  fall- 
ing through  a  vertical  shaft,  is  delivered 
to  alternating-current  circuits  for  transmis- 
sion. 

In  the  case  of  a  powerful  stream  like 
Niagara,  since  it  would  be  impossible  to 
set  a  wheel  at  the  foot  of  the  falls,  tur- 
bines are  placed  at  the  bottom  of  a  pit 
178  feet  deep,  situated  a  mile  and  a  half 
up  the  river.  The  water  that  falls 
through  the  penstocks  is  discharged 
through  a  tunnel  at  the  foot  of  the  falls. 
The  total  available  capacity  of  the  tunnel 
is  about  100,000  horse-power. 

The  capacity  of  each   turbine  is  5,000 


QQ 


rfl 


§  a 


SI 


THE   TRANSMISSION 

horse-power  at  the 
Consequently,  it  would  be  necessary  to 
install  20  turbines  in  all  in  order  to  utilize 
the  full  capacity  of  the  tunnel.  Fig.  90 
gives  a  bird's-eye  view  of  the  arrangement 
with  the  wheel  pit  and  tunnel  in  section. 
Fig.  91,  shows  the  short  canal  leading  in 
from  the  river,  and  feeding  the  various 
wheels  through  their  separate  penstocks. 
P  P  P,  is  the  penstock,  or  vertical  iron 
feed  water  pipe  through  which  the  water 
falls  on  to  the  turbine.  T,  is  the  turbine, 
R  R,  the  tail  race,  that  is  a  large  exit 
pipe  through  which  the  water  passes  to 
the  tunnel  after  leaving  the  turbine.  The 
tunnel  is  7,250  feet  long,  14  to  18  feet 
wide,  and  21  feet  in  height,  its  gradient 
being  about  1  in  150.  Since  a  part  of  the 
tunnel  passes  under  the  city  of  Niagara  it 
was  necessary  to  prevent  all  possibility  of 
eroding  the  walls.  In  order  to  effect  this, 


314 


THE   ELECTRIC   MOTOR   AND 


the  entire  tunnel 
was  lined  with  vit- 
rified brick,  and 
about  13  millions 
of  bricks  were  used 
for  this  purpose. 
8,  S,  is  the  turbine 
shaft,  which  drives 
the  generator  6r,  in 
the  power  house 
above. 

An  inspection  of 
Fig.  92  will  show 
in  greater  detail 


K 


FIG.  91.— WHEEL  PIT. 


THE   TRANSMISSION    OF   POWER. 


315 


the  manner  in  which  the  lower  end 
of  the  penstock  delivers  its  \vater  to 
the  turbine  wheel.  After  falling  through 


FIG.  92.— ONE  OF  THE  NIAGARA  POWER  COMPANY'S  5,000 
HP  TURBINES  DESIGNED  BY  FAESCH  <fe  PICCARD, 
GENEVA,  SWITZERLAND.  BUILT  BY  THE  I.  P.  MORRIS 
COMPANY,  PHILADELPHIA,  PA. 

the  vertical  pipe  P,  P,  of  Fig.  91,  it 
passes  through  the  inclined  pipe  P,  P, 
at  the  lower  part  of  the  penstock,  entering 
the  body  of  the  turbine  at  rl]  and  is  dis- 


316 


THE   ELECTRIC    MOTOR   AND 


charged  therefrom  into  the  tail  race  below. 
The  vertical  axis  of  the  shaft  of  the  tur- 


FIG.  93.— SECTION  OF  THE  TUHBINE. 

bine  AS;  passes  upwards  to  the  generator,  as 
shown  more  completely  in  Fig.  91. 


THE  TRANSMISSION   OF   POWER.          317 

A  vertical  section  to  the  parts  shown  in 
Fig.  92,  is  given  in  Fig.  93,  together  with 
the  upper  portion  of  the  penstock  and 
turbine  shaft.  In  this  figure  the  same 
letters  refer  to  the  same  parts. 

Coming  to  the  top  of  the  turbine  shaft, 
we  find  the  generator  which  it  drives.  In 
this  form  of  generator  it  is  the  field  mag- 
nets which  move,  the  armature  remaining 
at  rest.  The  armature  is  shown  in  Fig. 
94.  A,  A,  is  the  Gramme-ring  diphase 
armature  of  the  iron-clad  type,  resting 
upon  the  pedestal  JP,  and  having  187  slots 
cut  in  its  surface  in  which  the  conductors 
are  placed.  There  are  two  conductors  in 
each  slot,  each  conductor  formed  of  a 
copper  bar  1.34"  X  0.44"  in  cross-section. 
The  winding  of  the  armature  is  in  two 
separate  circuits,  so  arranged  that  the 
alternating  E.  M.  F.  is  generated  one 


318 


THE  ELECTRIC   MOTOR  AND 


quarter  of  a  wave  apart  in  the  two  cir- 
cuits, so  that  the  two  E.  M.  Fs.  are  in 
diphase  relationship. 


FIG.  94. — ONE  OF  THE  5,000  HP  ARMATURES. 

The  revolving  field  ring,  with  its  12 
poles,  is  represented  separately  in  Fig.  95. 
The  poles  N,  /#,  are  of  soft  steel,  rigidly 


THE   TRANSMISSION   OF   POWER.  319 

bolted  on  the  interior  of  the  solid  nickel 
steel  ring,  and  the  field  spools  are  repre- 
sented in  position.  These  field  coils  are 
wound  on  brass  spools  and  are  all  perma- 


FIG.  95.— FIELD  RING  WITH  POLES  AND  BOBBINS  IN  PLACE. 

nently  excited  by  a  continuous  current 
from  a  separate  generator.  The  field  ring 
is  11'  7"  in  diameter,  and  revolves  at  250 
revolutions  per  minute.  The  cover  of  the 
field  ring  is  shown  in  an  inverted  position 


320  THE   ELECTRIC   MOTOR   AND 

in  Fig.  96.  A,  A,  A,  are  ventilating  aper- 
tures in  the  cover,  intended  to  draw  in 
cool  air  for  the  ventilation  of  the  armature 
during  rotation,  while  C,  is  a  central  aper- 
ture for  the  reception  of  the  turbine  shaft. 


FIG.  96. — THE  DRIVER  FOR  THE  FIELD  RING. 

Since  the  field  magnets  revolve  around 
the  fixed  armature,  it  is  necessary  to 
firmly  attach  the  field  to  the  shaft.  This 
is  effected  by  means  of  the  cover  just  de- 
scribed. A  completed  machine  is  repre- 
sented in  position  in  Fig.  97. 

A  vertical    cross-section  of  the  machine 


THE   TRANSMISSION    OF   POWER. 


321 


tli rough  the  axis  of  the  shaft  is  shown  in 
Fig.  98.  s,  ,y,  $,  is  the  turbine  shaft  to  the 
top  of  which  is  firmly  secured  the  moving 


FIG.  97.— THE  FIRST  GENERATOR  IN  POSITION  IN  THE 
POWER  HOUSE  AT  NIAGARA. 


field  ring  F.  H.,  through  the  driver  D. 
The  poles  p,  p,  have  their  coils  excited  by 
current  supplied  through  the  collector  rings 


322  THE   ELECTRIC    MOTOR   AND 

$     Brushes,  not  shown  in  the  figure,  rest 
on  these  rings,    supported    on   the   brush 


FIG.  98.— VERTICAL  SECTION  OP  ONE  OF  THE  5,000  HP 
GENERATORS. 

holder  bars  b,  b,  attached  to  the  platform 
over  the  machine.    The  current  is  supplied 


THE  TRANSMISSION   OF   POWER.  323 

to  these  brush  holders  through  conductors 
6r,  leading  to  an  independent  generator  at 
175  volts  pressure,  a,  a,  is  the  fixed 
armature  ring  supported  on  the  cast-iron 
base  B. 

The  electric  connections  necessary  for 
the  local  and  long  distance  distribution  of 
power  are  represented  in  Fig.  99,  for  two 
5,000  horse-power  generators.  The  pres- 
sure supplied  by  the  alternators  in  each  of 
their  two  separate  diphase  circuits  is  from 
2,000  to  2,400  volts,  according  to  require- 
ments. The  two  generators  are  indicated 
at  1  and  2.  Their  four  wires  are  led  to 
separate  switches  8 and  S".  Each  switch 
is  arranged  so  that  it  can  either  be  discon- 
nected altogether,  as  shown  in  the  diagram, 
or  can  make  connection  between  the  gener- 
ator and  either  of  the  sets  of  bus-bars  A 
and  B.  Thus,  if  the  switch  be  thrown  on 


324 


THE   ELECTRIC   MOTOR  AND 


one  side,  it  will  connect  the  four  generator 
wires  to  the  four  bus-bar  wires  A,  while 


FIG.  99. — DIAGRAM  SHOWING  THE  CONNECTIONS  OF 
THE  GENERATORS  WITH  LOCAL  AND  LONG  DISTANCE 
FEEDERS. 

if  it  be  thrown  on  the  other  side,  it  will 
connect  the  generator  wires  to  the  four 
bus-bar  wires  B. 


THE   TRANSMISSION   OF   POWEK.  325 

The  two  sets  of  bus-bars  are  arranged  so 
as  to  enable  the  two  separate  generators 
to  be  employed  independently  ;  one,  for  ex- 
ample, to  supply  local  distribution,  and  the 
other,  to  supply  long  distance  distribution. 
The  switch  8'  8',  in  the  centre  of  the  figure, 
enables  connection  to  be  made  between  the 
long  distance  wires  Z,  and  the  bus-bars  B, 
or  the  local  circuit  wires  L,  L',  and  the  bus- 
bars A.  For  local  distribution,  a  pressure 
of  2,000  volts  is  sufficient  without  the  inter- 
vention of  any  step-up  transformers ;  but 
for  long  distance  transmission,  as,  for 
example,  to  Buffalo,  the  step-up  trans- 
formers T,  T',  would  be  employed.  These 
are  so  arranged,  that  when  connected  in 

o         ' 

the  proper  manner,  having  their  pri- 
maries supplied  by  diphase  currents,  their 
secondaries  will  generate  tri phase  currents. 
The  three  long-distance  mains  are  rep- 
resented on  the  secondary  side.  This 


326  THE   ELECTRIC    MOTOR   AND 


FIG.  100. — THE  INTERNAL  CONSTRUCTION  OF  A  LARGE 
STATIC  TRANSFORMER.  THIS  TRANSFORMER  REDUCES 
THE  PRESSURE  OF  THE  TWO-PHASE  ALTERNATING 
CURRENT  FROM  2,400  TO  200  VOLTS. 


transfer  from  the  diphase  to  the  triphase 
system  is  introduced  for  the  purpose  of 
saving  copper  in  the  line  transmission. 


THE   TRANSMISSION   OF   POWER.          327 


FIG.  101.— 1,000  HP  TRANSFORMER. 


328  THE   ELECTRIC    MOTOR. 

Fig.  100,  shows  the  internal  parts  of  a 
large  1,000  horse-power  transformer,  in- 
tended for  the  reduction  of  pressure  from 
2,200  to  200  volts,  but  it  would,  of  course, 
be  possible  to  employ  similar  transformers 
for  raising  the  pressure,  the  secondary 
windings  then  being  altered.  This  trans- 
former belongs  to  the  type  of  oil-cooled 
transformers.  It  is  set  in  an  iron  case, 
represented  in  Fig.  101,  through  which  oil 
is  pumped. 

An  excellent  illustration  of  the  capa- 
bilities of  long-distance  alternating-current 
transmission  is  seen  in  Fig.  102.  Here  the 
power  station,  which  might  be  a  station  like 
that  at  Niagara  Falls,  is  represented  in  the 
lower,  left-hand  corner,  with  triphasers 
driven  by  water-wheels  and  supplying  a 
pressure  of  2,000  volts.  The  pressure  is 
raised  to  10,000  volts  by  means  of  three 


0 

!,; 

£ 

ill 

{ 

ow  £ 

3  S 

~     DD 

14 

H  § 

^  r 

>•   *~* 

5  « 

0!       $ 

^       ^ 

L 

i  ^ 

S 

3  H 
§  P 

>  s 

^    ^3 

a  w 

3   0 

33   * 

2? 

§§ 

13 

^  3 

hi 

aj 

o 

a 

330 


THE   ELECTRIC    MOTOR   AND 


step-up  transformers,  and  is  transmitted 
through  the  three  long-distance  wires  to 
the  receiving  station,  where  it  is  reduced 


FIG.  103. — A  TYPICAL  ALTERNATING-CURRENT  INDUCTION 
MOTOR  OF  125  HP. 

through  step-down  transformers  to  a  pres- 
sure of  310  volts,  in  a  circuit  intended  for 
street  railway  power  transmission,  and  to 
2,000  volts,  in  another  circuit  intended  for 


THE  TRANSMISSION   OF  POWER.  331 

city  distribution.  The  3 10- volt  triphase- 
circuit  is  led  to  a  rotary  converter  /  i.  e.,  a 
triphase  motor  carrying  a  commutator  upon 
which  brushes  rest  in  such  a  manner  that 
as  the  motor  armature  revolves,  the  alter- 
nating current  received  at  the  collector 
rings  on  one  side  is  redistributed  through 
the  commutator  as  a  continuous  current 
of  500  volts  pressure  on  the  other,  which 
pressure  is  conveyed  to  the  street  railway 
mains.  The  2,000-volt  secondary  circuits 
are  carried  through  the  city,  and  are  either 
employed  to  drive  triphase  motors  of  the 
synchronous  or  non-synchronous  type,  or 
through  local  transformers  to  distribute 
light  and  power  in  110-volt  triphase  or 
Uniphase  circuits. 

A  form  of  triphase  motor  of  125  horse- 
power, or  about  94  KW,  is  represented  in 
Fig.  103.  Here  the  current  is  supplied 


332 


THE   ELECTRIC    MOTOR   AND 


through  three  terminals  at  the  top  of  the 
field  frame.  The  armature  carries  a  collar 
which  is  so  arranged  that  when  disengaged 


FIG.  104.— A  250-HP  THREE-PHASE  ALTERNATING- 
CURRENT  MOTOR. 


from  its  receptacle,  a  certain  resistance  is 
inserted  in  the  armature  circuit,  but  when 
the  motor  has  attained  full  speed,  the  collar 


THE   TRANSMISSION   OF   POWER.  333 

is  thrown  into  its  receptacle  by  the  use  of 
the  projecting  handle  at  the  side,  when 
this  resistance  is  cut  out  of  the  armature 
circuit. 

Fig.  104,  represents  a  form  of  more 
powerful  tri phase  motor,  being  adapted 
to  supply  250  HP,  or  about  188  KW. 
Here  the  current  is  supplied  through 
the  three  collector  rings  of  the  rotat- 
ing portion  or  rotor.  This  produces 
a  rotating  field  in  the  armature,  under 
the  action  of  which  the  armature  attracts 
the  field  frame  and  is  set  in  rotation. 
After  the  armature  has  reached  full 
speed  the  machine  acts  as  a  synchronous 
motor  in  step  with  the  triphase  impulses 
received  on  the  line. 

If  the  motor  were  a  uniphase  machine,  it 
would  not  be  able  to  start  itself  from  a 


334  THE   ELECTRIC   MOTOR. 

state  of  rest,  but  once  brought  to  full 
speed  it  would  also  be  able  to  run  in 
synchronism,  although  it  would,  probably, 
be  more  easily  thrown  out  of  step  by  a 
sadden  variation  of  load. 

The  torque  which  a  multiphase  ;  that  is, 
of  a  diphase  or  triphase  induction  motor, 
can  exert  at  starting;  i.  e.,  its  starting 
torque,  is  often  considerably  greater  than 
the  torque  which  it  will  have  to  exert 
when  running  at  full  speed  under  full  load. 
The  starting  torque  of  a  multiphase  syn- 
chronous motor  is  usually  much  less  than 
its  full  load  torque,  but  its  power  factor 
at  full  load  is  greater  than  that  of  an 
induction  motor.  This  is  often  an  advan- 
tage to  the  alternating-current  distributing 
system. 


CHAPTER  XII. 

MISCELLANEOUS    APPLICATIONS    OF    ELECTRIC 
MOTORS. 

ONE  of  the  principal  advantages  of  the 
electric  motor  is  the  ease  with  which  it 
can  be  directly  applied  to  machinery.  It 
has  been  customary,  in  large  machine 
shops,  to  employ  long  lines  of  shafting, 
receiving  power  from  an  engine  or  other 
prime  mover,  and  transmitting  this  power 
to  the  driving  pulleys  of  machines,  either 
directly,  or  through  the  intervention  of 
counter-shafts.  The  use  of  the  electric 
motor  enables  each  machine  to  be  operated 
independently  of  all  the  others,  thus 
avoiding  the  continuous  expenditure  of 


330  THE   ELECTRIC    MOTOR   AND 

power  in  overcoming  the  friction  of  line 
shafts.  Moreover,  the  requirements  of 
each  machine  as  to  speed  and  regulation 
may  be  more  readily  dealt  with  by  this 
means.  In  some  cases,  where  machinery 
lias  to  stand  at  an  angle  with  the  line 
shafting,  the  difficulty  which  would  be 
experienced  in  belting  to  the  same  are 
entirely  overcome.  In  other  cases  groups 
of  machines  may  be  operated  each  from  a 
single  motor,  by  the  use  of  short  lengths  of 
counter-shaft.  This  is  known  as  the  group 
system. 

,  The  number  of  machines  to  which  elec- 
tric motive  power  has  been  applied  is  so 
great  that  space  will  prevent  more  than 
a  cursory  description  of  them.  We  will, 
therefore,  select  some  of  the  more  promi- 
nent of  these  applications,  although  many 
others  will  occur  to  the  reader. 


THE   TRANSMISSION    OF   POWER.  337 

The  application  of  the  electric  motor  to 
the  driving  of  a  screw  machine  is  shown 


FIG.  105.— ELECTRIC  MONITOR  OR  SCREW  MACHINE. 

in  Fig.  105.  Here  the  armature  of  the 
electric  motor,  mounted  on  the  lathe 
head,  is  shown  at  A.  A  switch  is  pro- 


338 


THE  ELECTRIC   MOTOll   AND 


vided  at  S,  for  starting  the  motor,  which, 
is  an  ordinary  continuous-current  machine. 

Fig  106,  shows  the  application  of  a  con- 
tinuous-current   electric     motor     directly 


FIG.  106. — ELECTRIC  PIPE  CUTTING  MACHINE. 


coupled  to  a  pipe  cutting  machine.  Fig. 
107,  shows  the  application  of  a  continuous- 
current  electric  motor,  to  a  punch  press. 


THE  TRANSMISSION   OF  POWER,  339 

Here  the  motor  is  geared  to  the  shaft  of 
the  machine.  « 

The  electric  motor  is  particularly 
adapted  for  driving  such  machinery  as  is 
used  at  irregular  intervals,  and  where  but 
little  power  is  required.  Of  course,  under 
these  circumstances,  it  would  not  be 
economical  to  install  a  steam  engine 
and  boiler.  An  instance  of  this  kind  is 
found  in  the  driving  of  the  bellows  of 
church  organs.  Water  motors,  formerly 
employed  for  this  purpose,  have  been 
largely  superseded  by  electric  motors. 
An  electric  motor  attached  to  a  house  or 
church  organ  is  represented  in  Fig.  108. 
M,  is  a  small  continuous-current  motor, 
belted  to  the  pulley  of  the  bellows 
mechanism.  A  regulator  7?,  is  so  ar- 
ranged, that  if  the  rate  of  pumping  is  not 
sufficient  to  maintain  the  full  wind  pres- 


340 


THE   ELECTRIC    MOTOR   AND 


sure,  a  resistance  will  be  cut  out  of  the 
circuit  and  the  motor  will  be  accelerated. 
The  starting  box  S,  is  placed  by  the  side 


I     1*1 

I  ,v~—  1 


FKL  107.— ELECTRIC  PUNCH  PRESS  WITH  DIVIDING 
HEAD  OR  INDEX. 


of  the  keyboard,  so  as  to  permit  the  organ- 
ist readily  to  start  and  stop  the  motor  at 
will. 


THE   TRANSMISSION    OF   POWER.  341 


FIG.  108. — ELECTRIC  MOTOR  APPLIED  TO  ORGAN 
BELLOWS. 

The  application  of  the  electric  motor  to 
the  pumping  of  water  is  shown  in  Fig. 
109,  Here  a  continuous-current  motor  M 


342  THE   ELECTRIC   MOTOR  AND 


<  109.— ELECTRIC  MOTOR  APPLIED  TO  PUMPING  IN 
DWELLING  HOUSE. 


THE  TRANSMISSION   OF   POWER.  343 

operated  from  incandescent  electric  light 
mains,  is  belted  to  the  pump  pulley.  The 
supply  wires  to  the  motor  are  led  through 
a  fuse  block  F,  to  the  double-pole  snap 
switch  S,  from  which  they  proceed  to  an 
automatic  switch.  This  latter  is  provided 
for  the  stopping  and  starting  of  the  motor, 
under  the  control  of  a  ball  float  in  a  water 
tank.  When  the  water  in  the  tank 
reaches  a  certain  height,  the  rising  of  the 
ball  lowers  the  weight  and  suddenly  opens 
the  armature  circuit.  On  the  contrary, 
when  the  water  in  the  tank  falls  too  low, 
the  descent  of  the  float  raises  the  weight, 
and  starts  the  motor  slowly.  In  all  such 
cases,  where  motors  are  installed  under 
conditions  where  they  are  likely  to  run 
for  weeks  without  attention,  it  is  advisable 
to  employ  motors  of  as  slow  a  speed  and 
substantial  a  construction  as  possible,  so  as 
to  diminish  the  wear  and  tear,  and  hence 


344  THE   ELECTRIC    MOTOR   AND 

the  attention  required.  It  is,  for  this 
reason,  even  advisable  to  employ  a  motor 
of  more  than  sufficient  size  to  do  the  work 
required,  since  under  these  circumstances 
it  will  run  with  very  little  effort. 

The  motors,  above  illustrated,  have 
been  all  of  the  continuous-current  type. 
It  is  needless  to  say,  however,  that  alter- 
nating-current motors  could  be  employed 
in  their  stead,  provided  that  they  are  of 
the  multiphase  type,  so  as  to  permit  them 
to  start  from  rest. 

Fig.  110  shows  a  Gatling  gun,  in  which 
an  electric  motor  is  employed  for  the  pur- 
pose of  operating  the  breech  mechanism. 
The  certainty  and  precision  with  which 
the  motor  will  introduce  and  release  the 
cartridges,  renders  this  application  of  the 
electric  motor  very  advantageous. 


THE   TRANSMISSION 


The  applications  of  the 
for  prospecting  in  mining  districts 
known.     The  electric  motor   provides   an 


FIG.  110.— GATLING  GUN.     OPERATED  BY  ELECTRIC 
MOTOR. 

exceedingly  convenient  means  for  driving 
such  drills,  when  electric  power  is  avail- 
able. Their  use  in  mining  districts  has 


346 


THE   ELECTRIC    MOTOR    AND 


come  into  favor,  owing  to  the  fact  that  the 
solid  core  of  the  rock  mined  is  brought 
out  by  this  drill.  Fig.  Ill,  shows  a  form 


FIG.  111. — ELECTRIC  DIAMOND  PROSPECTING  DRILL. 

of  this  machine  with  a  continuous-current 
electric  motor  applied  to  drive  it. 

Electric  motors  are  often  applied  both 


THE   TRANSMISSION    OF   POWER.  347 

to  elevators  in  buildings,  and  to  hoists  in 
mines.     In   the   latter  case,  the  ease  with 


FIG.  112. — THOMSON-HOUSTON  PORTABLE  ELECTKIC 
HOIST.     BAND  CLUTCH  TYPE. 

which  the  power  can  be  carried  to  different 
parts  of  the  mine  renders  the  electric  driv- 
ing of  such  hoists  very  advantageous.  An 


348  THE   ELECTRIC    MOTOR   AND 

illustration  of  a  continuous-current  motor, 
connected  with  a  portable  electric  hoist,  is 


FIG.  113.— AN  ALTERNATING-CURRENT  INDUCTION 
MOTOR  GEARED  TO  A  HOIST. 

shown  in  Fig.  112.  A  similar  form  of 
hoist  driven  by  an  alternating-current 
induction  motor  is  shown  in  Fig.  113, 


THE  TRANSMISSION    OF   POWER. 


349 


In  the  commercial  sale  of  electric  power, 
whether  for  lighting  or  for  motive  pur- 
poses, a  necessity  exists  for  carefully 


FIG.  114— 1/8  HP  ELECTRIC  FAN.    WITH  WIRE  GUARD 
AND  SWITCH  FOR  RUNNING  FAST  OR  SLOW. 


measuring  the  amount  of  supply  to  each 
consumer.  For  this  purpose  a  variety  of 
electric  meters  are  employed.  The  electric 
meters  commonly  in  use  employ  a  small 


350 


THE   ELECTRIC   MOTOR  AND 


motor  driven  by  the  electric  power,  at  a 
speed  proportionate  to  the  rate  of  supply. 

Probably  there  is  no  purpose  for  which 
small   powers   are   more   required   during 


FIG.  115. — FAN  MOTOR. 


certain  seasons  of  the  year,  than  for  driving 
rotary  fans.  A  great  variety  of  forms  have 
been  devised,  varying  not  only  with  the 
character  of  the  fan,  but  also  with  the  posi- 


THE   TRANSMISSION   OF   POWER.  351 

tion  in  which  it  is  located.  Fan  motors 
are  made  to  operate,  both  on  continuous 
and  on  alternating-current  circuits.  For 


FIG.  116. — FAN  MOTOR  BRUSHES  IN  DETAIL. 

such  small  alternating-current  motors  mul- 
tiphase circuits  are  not  required.  A 
fan  motor  always  starts  with  no  load,  be- 


352 


THE   ELECTRIC    MOTOR   AND 


yond  the  friction  of  its  own  bearings, 
but  the  load  increases  rapidly  as  the 
speed  increases,  the  activity  developed 
being,  approximately,  as  the  cube  of  the 


FIG.  117.— No.  3  FAN  MOTOR. 

velocity.  The  fan  is  generally  attached 
directly  to  the  motor  shaft.  Fig.  114  is 
an  illustration  of  a  continuous-current  fan 
motor,  arranged  for  various  speeds.  Here, 


THE   TRANSMISSION    OF   POWER.  353 

as  is  usual  where  the  motor  is  in  a  position 
in  which  it  may  be  touched,  it  is  provided 
with  a  wire  guard. 


FIG.  118.— No.   1  FAN  OUTFIT  FOR  ARC   CIRCUITS 
(CONSTANT  CURRENTS). 

The  motor  described  in  Fig.  114  is  ex- 
posed to  view.  Frequently,  however,  the 
motor  is  inclosed  in  a  cast-iron  case,  as 
shown  in  Fig.  115.  In  such  cases  special 
attention  has  to  be  paid  to  the  brushes  and 


354 


THE   ELECTRIC   MOTOR   AND 


commutator,  since  they  run  out  of  view. 
Fig.  116,  shows  the  details  of  a  form  of 


FIG.  119. — CEILING  FAN  AND  MOTOR. 


brush  employed  in  the  motor  of  Fig.  115. 
Here,  it  will  be  seen  that  carbon  cylindri- 
cal brushes  are  employed  which  are  main- 


THE   TRANSMISSION    OF   POWER.  355 

tained  in  pressure  upou  the  commutator  by 
the  action  of  a  spiral  spring. 

Fig.   117,    shows  an  alternating-current 


FIG.  120.— No.  2  (1/4  HP)  FAN  OUTFIT,  SET  UP  AS  AN 
EXHAUST. 


fan  motor,  also  enclosed.  Fig.  118,  shows 
a  form  of  fan  motor  intended  to  be  oper- 
ated on  a  series-arc  circuit.  Since  the 
pressure  employed  on  such  a  circuit  is 


356  THE   ELECTRIC   MOTOR   AND 

generally  high,  this  motor  requires  to  be 
carefully  insulated. 

For  the  cooling  of  rooms,  the  fans  are 


FIG.  121.— DIRECT-CONNECTED   EXHAUST  FANS  AND 
LUNDELL  MOTORS. 


sometimes  suspended  from  the  ceilings. 
In  this  case  the  fan  blades  are  driven  in  a 
horizontal  plane  by  a  suitably  supported 
motor.  Fior.  119,  shows  a  form  of  ceiling 


THE  TRANSMISSION   OF   POWER.          357 


FIG.  122. — ELECTRIC  CAPSTANS. 


358  THE   ELECTRIC    MOTOli. 

fan  motor,  adapted  for  continuous-cunvnt 
circuits.  Here  the  motor  is  placed  below 
the  fau  blades. 

The  electric  motor  is  frequently  used  for 
ventilating  purposes.  In  Fig.  120  a  motor, 
is  shown  in  position  for  driving  an  exhaust 
fan.  Another  form  of  such  motor  is  shown 
in  Fig.  121. 

Fig.  122  shows  the  application  of  the 
electric  motor  for  driving  a  capstan  on 
board  ship.  In  this  particular  case  the 
motor  is  operated  on  a  110-volt  continuous- 
current  circuit,  and  has  a  capacity  of  about 
5KW. 


INDEX. 


Active  Conductor,  Circular  Flux  of,  84,  85. 
Activity,  11. 

of  Electric  Circuit,  53,  54,  55. 

of  Motor,  157,  158. 

,  Thermal,  55. 

,  Unit  of,  11,  12. 

— ,  Wasted,  55. 
Alternating-Current  Dynamo,  257,  258. 

Current  Motors,  241  to  283. 

Current  Transformers,  247. 

Current  Transmission,  302  to  334. 

—  E.  M.  F.,  242. 
Alternator,  257,  258. 

,  Collector  Rings  of,  258. 

.  Monocyclic,  275,  276. 

Ampere,  35. 

359 


360  INDEX. 

Ampere  Turns,  131. 

Analogue  of  Electric  Flow,  67  to  70. 

Armature  Core  of  Motor,  162. 

,  Monocyclic,  273. 

of  Motor,  110. 

,  Smooth-Core,  174,  175. 

,  Smooth -Core,  Completed,  179,  180. 

,  Toothed-Core,  174,  175. 

,  Toothed-Core,  Completed,  180. 

Armatures,  Disc,  171,  172,  173. 

,  Drum,  170. 

,  5,000  Horse-Power,  318. 

,  Ring,  170. 

Automatic  Self-Oiling  Bearings,  189,  190. 

B 

Babbitt  Metal,  188. 

Back  Pressure,  Electric,  49. 

Barlow,  94. 

Wheel  Motor,  95. 

Bar-Magnet,  Flux  of,  79. 
Battery,  Voltaic,  37. 

,  Voltaic,  Series-Connected,  38. 

Bearings,  Automatic  Self-Oiling,  189,  190. 
,  Self-Oiling,  163. 


INDEX.  361 

Belt  Tightener,  200. 

Bluestone  Voltaic  Cell,  36. 

Board  of  Trade  Unit,  160. 

Boiler  and  Steam  Engine,  Low  Efficiency  of,  26 

to  28. 

Box,  Cut-Out,  208. 
Broken  Circuit,  32. 
Brushes,  Adjustment  of,  211. 

,  Arrangement  of,  186. 

Brush  Holders,  187. 


c 

C.  E.  M.  F.,  49. 

Cell,  Bluestone  Voltaic,  36. 
Choking  Effect,  245. 
Circuit,  Broken,  32. 

— ,  Closed,  32. 

— ,  Completed,  32. 
,  Driven,  248. 

— ,  Driving,  248. 

— ,  Electric,  31,  32. 

,  Electric,  Activity  of,  53,  54,  55. 

,  Made,  32. 

,  Open,  32. 

,  Primary,  248. 


362  INDEX. 

Circuit,  Resistance  of,  34. 

,  Secondary,  248. 

-,  Uniphase,  305. 

Circular  Flux  of  Active  Conductor,  84,  85. 

Mil,  42. 

Mil-Foot,  42. 

Closed  Circuit,  32. 
Commutation,  Diameter  of,  164. 

,  Sparkless,  212. 

Commutator,  Two-Part,  184. 
Completed  Circuit,  32. 
Compound-Wound  Motor,  156,  157. 
Connections  of  Shunt-Wound  Motor,  207,  208. 
Conservation  of  Energy,  Doctrine  of,  2. 
Constant-Potential  Mains,  147. 
Continuous-Current  Motor,  Forms  of,  164  to  169. 

-  E.  M.  F-,  242. 
Converter,  Rotary,  331. 
Core  of  Motor  Armature,  162. 
Cores,  Laminated,  of  Motors,  176. 
Coulomb,  44. 

•  per-Second,  44. 

Counter  Electromotive  Force,  49,  59,  60. 
Current,  Alternating,  242. 

— ,  Electric,  30. 

•  Strength,  34. 

Strength  or  Flow,  Unit  of,  35. 


INDEX.  363 

Currents,  Eddy,  175,  176,  215,  216. 

,  Stray,  215,  216. 

Cut-Out  Box,  208. 
Cycle,  242. 

D 

Davenport,  104. 

Density,  Magnetic,  Unit  of,  134. 
Diagrams  of  Torque,  123,  124. 
Diameter  of  Commutation,  164. 
Diphase  Field,  292. 

Field-Frame,  292. 

,  Four-Conductor,  Diagram  of  System,  264, 

265. 

Four-Wire  Circuit,  306. 

,  Independent  Circuit,  307. 

Motor,  283. 

,  Three-Conductor  System,  266,  267. 

Three- Wire  System,  306. 

System,  263. 

— System,  Connections  of,  282. 

Disc  Armatures,  171,  172,  173. 

Dynamo,  Faraday's,  98  to  101. 

Double-Pole  Switch,  208. 
Driven  Circuit,  248. 
Driving  Circuit,  248. 


364  INDEX. 

Drop  or  Fall,  52. 

Drum  Armatures,  170. 

Dynamo,  Alternating-Current,  257,  258. 

Electric  Machine,  36,  37. 


E 

E.  M.  F.,  33. 

,  Continuous,  242. 

,  Effective,  144. 

Early  Faraday  Motor,  88,  89. 

Eddy  Currents,  175,  176,  215,  216. 

Effect,  Choking,  245. 

Effective  E.  M.  F.,  144. 

Resistance,  245. 

Efficiencies  of  Motors,  159,  213. 

Efficiency  of  Machine,  24,  25. 

Electric  and  Hydraulic  Resistance,  Analogy  Be- 
tween, 39,  40. 

Back  Pressure,  49. 

Circuit,  31,  32. 

Current,  30. 

Flow,  30. 

Motor,  Advantages  of,  217,  218. 

Motors,  Miscellaneous  Applications  of, 

335  to  358. 


INDEX.  3*35 

Electric  Pressure,  34. 

Sources,  30. 

Transmission,    Commercial     and    Electric 

Conditions  of  Problem,  223  to  240. 

Transmission  of  Power,  217  to  241. 

Electro-Dynamic  Force,  97,  120,  121,  122. 
Electromagnetic  Rotation,  76. 
Electromotive  Force,  33. 

Force,  Counter,  49. 

Force,  Unit  of,  35. 

Elias'  Motor,  108,  109. 
Energy,  Definition  of,  3. 

,  Doctrine  of  Conservation  of,  2. 

,  Hysteretic  Loss  of,  214. 

,  Indestructibility  of,  2. 

of  Food,  Transference  of,  8. 

,  Rate-of-Expending,  11. 

,  Sources  of,  19  to  28. 

Entrefer,  182. 
Ether  Streams,  81. 
,  Universal,  80,  81. 


F 


Factor,  Power,  254. 
Fan  Motors,  349  to  356. 


366  INDEX. 

Faraday,  74. 

Motor,  Early,  88,  89. 

Faraday's  Disc,  98  to  101. 
Field,  Magnetic,  77. 

Magnetic,  of  Motor,  110. 

Rheostat,  of  Motor,  210. 

,  Triphase  Rotating,  290,  291. 

Fields,  Diphase,  292. 

Five-Thousand  Horse-Power  Armature,  318. 

Flow,  Electric,  30. 

,  Electric,  Analogue  of,  67  to  70. 

Flux,  Leakage,  136. 

,  Magnetic,  77. 

,  Magnetic,  Unit  of,  131. 

,  Stray,  of  Motor,  136. 

Food,  Transference  of  Energy  of,  8. 
Foot-Pound,  9. 
Foot-Pound-per-Second,  12. 
Force,  Electro-Dynamic,  97,  120,  121,  122. 

,  Electromotive,  33. 

,  Magnetomotive,  130. 

Forward  Lead  of  Motor  Brushes,  212. 
Four- Wire  Diphase  Circuit,  306,  307. 
Frequency,  243. 
Froment's  Motor,  114,  115. 
Fuse,  Safety,  208. 


Gauss,  134. 
Gilbert,  131. 


INDEX.  367 

G 


H 

Holders,  Brush,  187. 
Horse-Power,  12. 

Hydraulic   Flow,    Gradient   of   Water    Pressure 
During,  61,  62. 

Transmission,  15. 

Hysteresis,  214. 
,  Magnetic,  214. 


Impedance,  247. 

Independent  Circuit,  Diphase,  307. 
Indestructibility  of  Energy,  2. 
Induction  Motor,  279. 

Motors,  289. 

Multiphase  Motors,  289. 

Installation  and  Operation  of  Motors,  200  to  216. 

of  Shunt- Wound  Motor,  205,  206. 

Intake  of  Machine,  22. 
Inter-Linked  Diphase,  307. 
International  Unit  of  Work,  9. 


368  INDEX. 

J 

Jacoby's  Electric  Motor,  101  to  104, 
Joule,  Definition  of,  9,  10. 
Joule-per-Second,  12,  48. 


Laminated  Cores  of  Motors,  176. 

Law,  Ohm's,  35. 

Lead,  Forward,  of  Motor  Brushes,  212. 

Leads,  52. 

Leakage  Flux,  136. 

,  Magnetic,  136. 


M 

M.  M.  F.,  131. 

Machine,  Dynamo-Electric,  36,  3V. 
— ,  Efficiency  of,  24. 

,  In-Take  of,  22. 

— '• ,  Multipolar,  113. 

,  Output  of,  23. 

,  Sextipolar,  113. 

Made  Circuit,  2. 


INDEX.  369 

Magnetic  Circuit  of  Motor,  28  to  130. 
-  Field,  77. 

—  Flux,  77. 
Hysteresis,  214. 

—  Leakage,  136. 

Resistance,  Unit  of,  132. 

Saturation,  134. 

Magnetism,  Rotary,  292. 
Magnetomotive  Force,  130. 

Force,  Units  of,  131. 

Mains,  Constant-Potential,  147. 

Microhms,  41. 

Mil,  42. 

Miscellaneous  Applications  of  the  Electric  Motor, 

335  to  358. 
Monocyclic  Alternator,  275,  276. 

Armature,  273. 

Armature  Winding,  273. 

System,  270  to  279. 

—  System,  Diagram  of  Distribution  by,  277, 

278. 
Motor,  Activity  of,  157,  158. 

Armature,  Core  of,  162. 

,  Armature  of,  110. 

Brushes,  Adjustment  of,  211. 

,  Circumstances  Affecting  Speed  of,  140  to 

143. 


370  INDEX. 

Motor,  Circumstances  Affecting  Torque  of,    138, 
139. 

,  Classification    of    Losses   of     Energy   in, 

213. 

,  Compound-Wound,  156,  157. 

,  Electric,  Advantages  of,  217,  218. 

,  Elementary  Theory  of,  119  to  161. 

— ,  Froment's,  114',  115. 
,  Induction,  279. 

— ,  Magnetic  Circuit  of,  128. 

,  Magnetic  Field  of,  110. 

-,  Multiphase  Induction,  294,  295. 

,  Quadripolar,  197. 

,  Separately-Excited,  111. 

,  Series- Wound,  154,  155. 

,  Shunt-Wound,  152,  153. 

Motors,  Alternating-Current,  242. 

,  Efficiency  of,  159,  160,  213. 

,  Fan,  349  to  356. 

,  Induction,  289. 

,  Installation    and    Operation    of,    200    to 

216. 

,  Synchronous  Multiphase,  289. 

Multiphase  Alternating-Current  System,  263. 

Induction  Motors,  289,  294,  295. 

Synchronous  Motors,  289. 

Multipolar  Machine,  113. 


INDEX.  371 

N 


Negative  Pole  of  Source,  31. 
Niagara  Transmission,  311  to  334. 


o 

Oersted,  90,  91,  132. 

Oersted's  Magnetic  Experiments,  90  to  93. 

Ohm,  35. 

Ohm's  Law,  35. 

Oil-Cooled  Transformer,  328. 

Open  Circuit,  32. 

Operation  and  Installation  of  Motors,  200  to  216. 

Output  of  Machine,  23. 


Pacinotti,  115. 

Pacinotti's  Motor,  116  to  118. 
Phase,  Displacement  of,  256. 
Pneumatic  Transmission,  15. 
Pole,  Negative,  of  Source,  31. 

,  Positive,  of  Source,  31. 

Positive  Pole  of  Source,  31. 

Power,  Electric  Transmission  of,  217,  241. 


372  INDEX. 

Power  Factor,  254. 

Houses,  220. 

Pressure,  Back,  Electric,  49. 

,  Drop  or  Fall  of,  52. 

— ,  Electric,  34. 
Primary  Circuit,  248. 


Q 

Quadripolar  Motors,  197,  198,  199. 
Quantity,  Electric,  Unit  of,  44. 

K 

Reactance,  243. 
Reluctance,  132. 

,  Specific,  135. 

Reluctivity,  135. 

Resistance,  Electric,  Unit  of,  35. 

of  Circuit,  34. 

,  Specific,  40. 

,  Total  Effective,  245. 

,  Unit  of,  35. 

Resisting  Torque,  143. 

Resistivity,  40. 

,  Effect  of  Temperature  on,  43. 


INDEX.  373 

Rheostat,  Field,  of  Motor,  210. 

,  Starting,  202,  203,  204. 

Ring  Armatures,  170. 
Ritchie,  105. 

Ritchie's  Motor,  106,  107. 
River,  Energy  of,  6. 
Rope  Transmission,  15. 
Rotary  Converter,  331. 

Magnetism,  292. 

Rotating  Field,  Triphase,  290,  291. 

Magnetic  Field,  284  to  301. 

Magnetic  Field,  Diagram  of,  285. 

Rotation,  Electromagnetic,  76. 
Rotor,  Definition  of,  110. 


s 

Safety  Fuse,  208. 
Saturation,  Magnetic,  134. 
Secondary  Circuit,  248. 
Separately-Excited  Motor,  111. 
Series-Connected  Voltaic  Battery,  38. 
Series  Connection,  37,  38. 
Series- Wound  Motor,  154,  155. 
Sextipolar  Machine,  113. 
Shunt- Wound  Motor,  152,  153. 


374  INDEX. 

Shunt- Wound  Motor,  Connections  of,  207,  208. 

,  Installation  of,  205,  206. 

Smooth-Core  Armature,  174,  175. 
Solar  Energy,  Varieties  of,  21,  22. 
Sources,  Electric,  30. 

of  Energy,  19  to  28. 

of  Energy,  Classification  of,  19. 

Sparkless  Commutation,  212. 
Specific  Reluctance,  135. 

•  Resistance,  40. 

Speed   of   Motor,   Circumstances    Affecting,    140 

to  143. 

Star  Connection  of  Triphaser,  308. 
Starting  Rheostat,  202,  203,  204. 
Stator,  Definition  of,  110. 

Steam  Engine  and  Boiler,  Efficiency  of,  26  to  28. 
Step-Down  Transformers,  250. 
Step-Up  Transformers,  251. 
Stray  Currents,  215,  216. 

Flux  of  Motor,  136. 

Stream  Lines,  81. 

Strength  of  Current,  34. 

Structure    and   Classification    of   Motors,   162   to 

199. 

Sturgeon,  96. 
Switch,  Double-Pole,  208. 
Synchronous  Multiphase  Motors,  289. 


INDEX.  375 

System,  Diphase,  263. 

,  Monocyclic,  270  to  279. 

,  Multiphase  Alternating-Current,  263. 

,  Triphase,  263,  264. 


Temperature,  Effect  of,  on  Resistivity  of  Metals, 

43. 

Theory,  Elementary,  of  Motor,  119,  120. 
Thermal  Activity,  55. 
Three- Wire  Diphase,  307. 
Toothed-Core  Armature,  174,  175. 
Torque,  Definition  of,  122. 

,  Diagrams  of,  123,  124. 

of   Motor,  Circumstances   Affecting,   138, 

139. 

,  Resisting,  143. 

Total  Effective  Resistance,  245. 
Transformer,  Alternating-Current,  247. 

,  Oil-Cooled,  228. 

Transformers,  247. 

,  Step-Down,  250. 

,  Step-Up,  251. 

Transmission,  Alternating-Current,  302  to  334. 
,  Hydraulic,  15. 


376  INDEX. 

Transmission  of  Power,  Electric,  217,  241. 

,  Pneumatic,  15. 

,  Rope,  15. 

,  Systems  of,  14. 

Triangle  Connection  of  Triphaser,  308. 
Triphase  Alternator,  269,  270. 

Motor,  297  to  299. 

,  Three-Wire  System,  268. 

,  Six-Wire  System,  267. 

System,  263,  264,  306. 

System,  Connections  of,  281. 

Triphaser,  267. 

Two-Part  Commutator,  184. 

Typical  Electric  Transmission  System,  219,  220. 

u 

Uniphase  Circuit,  305. 

Unit,  International,  of  Work,  9. 

of  Activity,  11,  12. 

of  Current  Strength  or  Flow,  35. 

of  Electric  Activity,  48. 

of  Electric  Quantity,  44. 

of  Electric  Work,  247. 

of  Electromotive  Force,  35. 

of  Magnetic  Density,  134. 

of  Magnetic  Resistance,  132. 


INDEX.  377 


Unit  of  Resistance,  35. 
Units  of  Magnetic  Flux,  131. 

of  Magnetomotive  Force,  131. 

of  Work,  9. 

Universal  Ether,  80,  81. 


V 

Varieties  of  Solar  Energy,  21,  22. 

Vertical  Section  of  5,000  Horse-Power  Generator, 

322. 

Voltage,  37. 
Volt,  35. 

Voltaic  Battery,  37. 
Volt-Coulomb,  47. 


w 

Wasted  Activity,  35. 

Watermotive  Force,  60,  61. 

Watt,  12,  48. 

Weber,  131. 

Winding,  Teaser,  of  Monocycler,  272. 

Work,  International  Unit  of,  9. 

— ,  Rate-of-Doing,  11. 
• ,  Units  of,  9, 


Elementa 
Electro  -  Technical 


B? 

EDWIN  J,  HOUSTON,  Ph.D,  and  A,  E.  KENNELLY,  D.Sc. 


Alternating  Electric  Currents,  Electric  Incandescent  Light- 
Electric  Heating,  ing, 

Electromagnetism,  Electric  Motors, 

Electricity  in  Electro-Thera-  Electric  Street  Railways, 

peutics,  Electric  Telephony, 

Electric  Arc  Lighting,  Electric  Telegraphy. 


Cloth,  profusely  illustrated.  Price,  $1.0O  per  volume. 


The  above  volumes  have  been  prepared  to  satisfy  a  demand 
which  exists  on  the  part  of  the  general  public  for  reliable  in- 
formation relating  to  the  various  branches  of  electro-technics. 
In  them  will  be  found  concise  and  authoritative  information  con- 
cerning the  several  departments  of  electrical  science  treated, 
and  the  reputation  of  the  authors,  and  their  recognized  ability 
as  writers,  are  a  sufficient  guarantee  as  to  the  accuracy  and 
reliability  of  the  statements.  The  entire  issue,  although  pub- 
lished in  a  series  of  ten  volumes,  is,  nevertheless  so  prepared  that 
each  volume  is  complete  in  itself,  and  can  be  understood  inde- 
pendently of  the  others.  The  books  are  well  printed  on  paper 
of  special  quality,  profusely  illustrated,  and  handsomely  bound 
in  covers  of  a  special  design. 

Copies  of  these  or  any  other  electrical  books  published  will  be  sent  by 
^  POSTAGE  PREPAID,  to  any  address  in  the  ivorld^  on  receipt  of  price. 


The  W.  J.  Johnston  Company,  Publishers, 

253  BROADWAY,  NEW  YORK. 


THIRD  EDITION.      GREA  TL  Y  ENLAR  GED 
A  DICTIONARY  OF 

Electrical  Words,  Terms, 
and  Phrases. 

By  EDWIN  J.  HOUSTON,  Ph.D.  (Princeton). 

AUTHOR  OF 

"Advanced  Primers  of  Electricity";    "Electricity   One 
Hundred  Years  Ago  and  To-day,"  etc.,  etc. 

Cloth,  667   large  octavo   pages,    582    illustrations, 
Price,  $5.00. 

Some  idea  of  the  scope  of  this  important  work  and  of  the  im- 
mense amount  of  labor  involved  in  it,  may  be  formed  when  it  is 
stated  that  it  contains  definitions  of  about  6000  distinct  words, 
terms,  or  phrases.  The  dictionary  is  not  a  mere  word-book  ;  the 
words,  terms,  and  phrases  are  invariably  followed  by  a  short,  can- 
cise  definition,  giving  the  sense  in  which  they  are  correctly  employed, 
and  a  general  statement  of  the  principles  of  electrical  science  on 
which  the  definition  is  founded.  Each  of  the  great  classes  or  di- 
visions of  electrical  investigation  or  utilization  comes  under  careful 
and  exhaustive  treatment ;  and  while  close  attention  is  given  to  the 
more  settled  and  hackneyed  phraseology  of  the  older  branches  of 
work,  the  newer  words  and  the  novel  departments  they  belong  to 
are  not  less  thoroughly  handled.  Every  source  of  information  has 
been  referred  to,  and  while  libraries  have  been  ransacked,  the  note- 
book of  the  laboratory  and  the  catalogue  of  the  wareroom  have  not 
been  forgotten  or  neglected.  So  far  has  the  work  been  carried  in 
respect  to  the  policy  of  inclusion  that  the  book  has  been  brought 
down  to  date  by  means  of  an  appendix,  in  which  are  placed  the 
very  newest  words,  as  well  as  many  whose  rareness  of  use  had  con- 
signed them  to  obscurity  and  oblivion. 

Copies  of  this  or  any  other  electrical  book  published  will  be  sent  by  mail, 
POSTAGE  PREPAID,  to  any  address  in  the  world ',  on  receipt  of  price. 


The  W,  J.  Johnston  Company,  Publishers, 

253  BROADWAY,  NEW  YORK. 


ELECTRICITY  AND  MAGNETISM. 

A  Series  of  Advanced  Primers. 

By  EDWIN  J.  HOUSTON,  PH.D.  (Princeton). 

AUTHOR   OF 

\ 

"A  Dictionary  of  Electrical  Words,  Terms  and 
Phrases"  etc.,  etc.,  etc. 

Gloth.    3O6  pages.  1 1 6  illustrations.    Price,  31. OO. 


During  the  Philadelphia  Electrical  Exhibition  of  1884,  Professor  Houston 
issued  a  set  of  elementary  electrical  primers  for  the  benefit  of  the  visitors  to 
the  exhibition,  which  attained  a  wide  popularity.  During  the  last  ten 
years,  however,  the  advances  in  the  applications  of  electricity  have  been  so 
great  and  so  widespread  that  the  public  would  no  longer  be  satisfied  with 
instruction  in  regard  to  only  the  most  obvious  and  simple  points,  and 
accordingly  the  author  has  prepared  a  set  of  new  primers  of  a  more  ad- 
vanced character  as  regards  matter  and  extent.  The  treatment,  neverthe- 
less, remains  such  that  they  can  be  easily  understood  by  anyone  without  a 
previous  knowledge  of  electricity.  Electricians  will  find  these  primers  of 
marked  interest  from  their  lucid  explanations  of  principles,  and  the  general 
public  will  find  in  them  an  easily  read  and  agreeable  introduction  to  a  fas. 
cinating  subject.  The  first  volume,  as  will  be  seen  from  the  contents, 
deals  with  the  theory  and  general  aspects  of  the  subject.  As  no 
mathematics  is  used  and  the  explanations  are  couched  in  the  simplest 
terms,  this  volume  is  an  ideal  first  book  from  which  to  obtain  the  prelimi- 
nary ideas  necessary  for  the  proper  understanding  of  more  advanced  works. 

Copies  of  this  or  any  other  electrical  book  published  will  be  sent  by 
POSTAGE  PREPAID,  to  any  address  in  the  world^  on  receipt  of  price. 


The  W.  J.  Johnston  Company,  Publishers, 

253  BROADWAY,  NEW  YORK. 


The  Measurement  of  Electrical  Cur- 
rents and  Other  Advanced 
Primers  of  Electricity. 

By  EDWIN  J.  HOUSTON,  PH.D.  (Princeton). 

AUTHOR  OF 

"  A    Dictionary    of   Electrical    Words,    Terms,    and 
Phrases"  etc.,  etc.,  etc. 

Cloth,     429  pages,  169  illustrations,     Price,  $1,00, 


This  volume  is  the  second  of  Prof.  Houston's  admirable  series 
of  Advanced  Primers  of  Electricity,  and  is  devoted  to  the  meas- 
urement and  practical  applications  of  the  electric  current.  The 
different  sources  of  electricity  are  taken  up  in  turn,  the  apparatus 
described  with  reference  to  commercial  forms,  and  the  different 
systems  of  distribution  explained.  The  sections  on  alternating 
currents  will  be  found  a  useful  introduction  to  a  branch  which  is 
daily  assuming  larger  proportions,  and  which  is  here  treated  with- 
out the  use  of  mathematics.  An  excellent  feature  of  this  series  of 
primers  is  the  care  of  statement  and  logical  treatment  of  the  sub- 
jects. In  this  respect  there  is  a  marked  contrast  to  most  popular 
treatises,  in  which  only  the  most  simple  and  merely  curious  points 
are  given,  to  the  exclusion  or  subordination  of  more  important 
ones.  The  abstracts  from  standard  electrical  authors  at  the  end  of 
each  primer  have  in  general  reference  and  furnish  an  extension  to 
some  important  point  in  the  primer,  and  at  the  same  time  give  the 
reader  an  introduction  to  electrical  literature.  The  abstracts  have 
been  chosen  with  care  from  authoritative  professional  sources  or 
from  treatises  of  educational  value  in  the  various  branches. 

Copies  of  this  or  any  other  electrical  book  published  will  be  sent  by  mail, 
POSTAGE  PREPAID,  to  any  address  in  the  world,  on  receipt  of  price. 


The  W.  J.  Johnston  Company,  Publishers, 

253  BROADWAY,  NEW  YORK. 


THE 

ELECTRICAL  TRANSMISSION  OF 
INTELLIGENCE, 

And  Other  Advanced  Primers  of  Electricity. 

By  EDWIN  J.  HOUSTON,  PH.D.  (Princeton). 

AUTHOR   OF 

"  A  Dictionary  of  Electrical  Words,  Terms  and 
Phrases"  etc.,  etc.,  etc. 

Cloth.      33O  pages,  88  illustrations.      Price,  31. OO. 


The  third  and  concluding  volume  of  Professor  Houston's  series  of 
Advanced  Primers  of  Electricity  is  devoted  to  the  telegraph,  telephone, 
and  miscellaneous  applications  of  the  electric  current.  In  this  volume  the 
difficult  subjects  of  multiple  and  cable  telegraphy  and  electrolysis,  as  well 
as  the  telephone,  storage  battery,  etc.,  are  treated  in  a  manner  that  en- 
ables the  beginner  to  easily  grasp  the  principles,  and  yet  with  no  sacrifice 
in  completeness  of  presentation.  The  electric  apparatus  for  use  in 
houses,  such  as  electric  bells,  annunciators,  thermostats,  electric  locks, 
gas-lighting  systems,  etc. ,  are  explained  and  illustrated.  The  primer  on 
electro-therapeutics  describes  the  medical  coil,  and  gives  instructions  for 
its  use,  as  well  as  explaining  the  action  of  various  currents  on  the  human 
body.  The  interesting  primers  on  cable  telegraphy  and  on  telephony  will 
be  appreciated  by  those  who  wish  to  obtain  a  clear  idea  of  the  theory  of 
these  attractive  branches  of  electrical  science,  and  a  knowledge  of  the  de- 
tails of  the  apparatus.  Attention  is  called  to  the  fact  that  each  of  the 
primers  in  this  series  is,  as  far  as  possible,  complete  in  itself,  and  that 
there  is  no  necessary  connection  between  the  several  volumes. 

Copies  of  this  or  any  other  electrical  book  published  will  be  sent  by 
mn.il ^  POSTAGE  PREPAID,  to  any  address  in  the  world,  on  receipt  of  price. 


The  W.  J.  Johnston  Company,  Publishers, 

253  BROADWAY,  NEW  YORK. 


ELECTRICITY 

One  Hundred  Years  Ago  and  To-Day. 

By  EDWIN  J.  HOUSTON,  PH.D.  (Princeton). 

AUTHOR  OF 

"A  Dictionary  of  Electrical  Words,  Terms  and 
Phrases"  etc.,  etc.,  etc. 

Cloth.          179  pages,  illustrated.         Price,  St. OO. 


In  tracing  the  history  of  electrical  science  from  practically  its  birth  to 
the  present  day,  the  author  has,  wherever  possible,  consulted  original 
sources  of  information.  As  a  result  of  these  researches,  several  revisions 
as  to  the  date  of  discovery  of  some  important  principles  in  electrical 
science  are  made  necessary.  While  the  compass  of  the  book  does  not 
permit  of  any  other  than  a  general  treatment  of  the  subject,  yet  numerous 
references  are  given  in  footnotes,  which  also  in  many  cases  quote  the 
words  in  which  a  discovery  was  first  announced  to  the  world,  or  give  more 
specific  information  in  regard  to  the  subjects  mentioned  in  the  main  por- 
tion of  the  book.  This  feature  is  one  of  interest  and  value,  for  often  a 
clearer  idea  may  be  obtained  from  the  words  of  a  discoverer  of  a  phenome- 
non or  principle  than  is  possible  through  other  sources.  The  work  is  not 
a  mere  catalogue  of  subjects  and  dates,  nor  is  it  couched  in  technical  lan- 
guage that  only  appeals  to  a  few.  On  the  contrary,  one  of  its  most  admir- 
able features  is  the  agreeable  style  in  which  the  work  is  written,  its 
philosophical  discussion  as  to  the  cause  and  effect  of  various  discoveries, 
and  its  personal  references  to  great  names  in  electrical  science.  Much  in- 
formation as  to  electrical  phenomena  may  also  be  obtained  from  the  book, 
as  the  author  is  not  satisfied  to  merely  give  the  history  of  a  discovery,  but 
also  adds  a  concise  and  clear  explanation  of  it. 

Copies  of  'this  or  any  other  electrical  book  published  will  be  sent  by 
mail,  POSTAGE  PREPAID,  to  any  address  in  the  -world,  on  receipt  of  price. 


The  W.  J.  Johnston  Company,  Publishers, 

253  BROADWAY,  NEW  YORK. 


THIRD  EDITION 


Alternating  Currents 

AN 

ANALYTICAL  AND  GRAPHICAL  TREATMENT 
FOR  STUDENTS  AND  ENGINEERS. 

BY 

FREDERICK  BEDELL,  Ph.D.,  and 
A,  C.  CREHORE,   Ph.D.,   (Cornell  University.) 


Cloth.    325  pages,  na  Illustrations.    Price,  $2.50. 


The  present  work  is  the  first  book  that  treats  the  subject  of 
alternating  currents  in  a  connected,  logical,  and  complete  manner. 
The  principles  are  gradually  and  logically  developed  from  the 
elementary  experiments  upon  which  they  are  based,  and  in  a 
manner  so  clear  and  simple  as  to  make  the  book  easily  read  by  any 
one  having  even  a  limited  knowledge  of  the  mathematics  involved. 
By  this  method  the  student  becomes  familiar  with  every  step  of 
the  process  of  development,  and  the  mysteries  usually  associated 
with  the  theory  of  alternating  currents  are  found  to  be  rather  the 
result  of  unsatisfactory  treatment  than  due  to  any  inherent  diffi- 
culty. The  first  fourteen  chapters  contain  the  analytical  develop- 
ment, commencing  with  circuits  containing  resistance  and  self- 
induction  only,  resistance  and  capacity  only,  and  proceeding  to 
more  complex  circuits  containing  resistance,  self-induction  and 
capacity,  and  resistance  and  distributed  capacity.  A  feature  is 
the  numerical  calculations  given  as  illustrations.  The  remaining 
chapters  are  devoted  to  the  graphical  consideration  of  the  same 
subjects,  enabling  a  reader  with  little  mathematical  knowledge  to 
follow  the  authors,  and  with  extensions  to  cases  that  are  better 
treated  by  the  graphical  than  by  the  analytical  method. 

Copies  of  this  or  any  other  electrical  book  published  will  be  sent  by  mail, 
POSTAGE  PREPAID,  to  any  address  in  the  world,  on  receipt  of  price. 


The  W,  J.  Johnston  Company,  Publishers, 

253  BROADWAY,  NEW  YORK. 


DYNAMO  AND  MOTOR  BUILDING 

FOR  AIVLATKURS. 

WITH   WORKING  DRAWINGS. 

By  LIEUT.  C.  D.  PARKHURST,  U,  S.  A. 
Cloth.      1 63  pages,  71  illustrations.     Price,  $1.00. 


One  of  the  most  fascinating  fields  for  the  amateur  is  that  af- 
forded by  electrical  science,  and  the  simplicity  of  construction  of 
small  dynamos  and  motors,  in  particular,  enables  him  not  only  to 
gratify  his  tastes,  but  at  the  same  time  to  construct  apparatus  that 
can  be  directly  applied  to  useful  purposes.  In  Parkhurst's  "  Dynamo 
and  Motor  Building  for  Amateurs  "  clear  and  concise  instructions, 
accompanied  by  working  drawings,  are  given  for  the  construction 
of  such  forms  and  types  of  dynamos  and  motors  as  are  simply  made 
and  yet  will  produce  fairly  efficient  results.  While  primarily 
intended  for  amateurs  and  students,  the  detailed  information, 
particularly  in  the  chapters  on  armature  windings,  connections, 
and  currents,  and  on  the  design  of  a  fifty-light  dynamo,  will  be  of 
value  to  every  electrician.  In  the  latter  chapter  the  subject  of  the 
proper  proportioning  of  the  armature  and  armature  wire,  the  cal- 
culation of  the  magnetic  circuit  and  field-windings,  etc.,  are  gone 
into  at  length,  and  in  the  light  of  the  most  recent  knowledge  and 
practice.  The  large  and  clear  drawings  showing  how  to  wind 
armatures  are  supplemented  by  tables,  so  that  the  beginner  will 
have  no  difficulty  whatever  in  carrying  out  the  instructions.  Every 
part  of  the  machines,  even  the  most  simple,  is  illustrated  and 
marked  with  its  dimensions. 

Copies  of  this  or  of  any  electrical  book  published  will  be  sent  by  mail, 
POSTAGE  PREPAID,  to  any  address  in  the  worldt  on  receipt  of  price. 


The  W.  J.  Johnston  Company,  Publishers, 

253  BROADWAY,  NEW  YORK. 


PUBLICATIONS  OF 

THE  W.  J.  JOHNSTON   COMPANY. 


The  Electrical  World.  An  Illustrated  Weekly 
Review  of  Current  Progress  in  Electricity  and  its  Prac- 
tical Applications.  Annual  subscription $3.00 

The  Electric  Railway  Gazette.    An  Illustrated 

Bi-monthly  Record  of  Electric  Railway  Practice  and 
Development.  Annual  subscription i.oo 

Johnston's  Electrical  and  Street  Railway 
Directory,  Containing  Lists  of  Central  Electric 
Light  Stations,  Isolated  Plants,  Electric  Mining  Plants, 
Street  Railway  Companies — Electric,  Horse  and  Cable— 
with  detailed  information  regarding  each  ;  also  Lists  of 
Electrical  and  Street  Railway  Manufacturers  and  Dealers,  • 
Electricians,  etc.  Published  annually 5.00 

The  Telegraph  in  America.  By  Jas.  D.  Reid. 
894  royal  octavo  pages,  handsomely  illustrated.  Russia,  7.00 

Dictionary  of  Electrical  Words,  Terms 
and  Phrases.  By  Edwin  J.  Houston,  Ph.D. 
Third  edition.  Greatly  enlarged.  667  double  column 
octavo  pages,  582  illustrations 5.00 

The  Electric  Motor  and  Its  Applications. 

By  T.  C.  Martin  and  Jos.  Wetzler.  With  an  appendix 
on  the  Development  of  the  Electric  Motor  since  1888,  by 
Dr=  Louis  Bell.  315  pages,  353  illustrations 3.00 

The  Electric  Railway  in  Theory  and 
Practice.  The  First  Systematic  Treatise  on  the 
Electric  Railway.  By  O.  T.  Crosby  and  Dr.  Louis 
Bell.  Second  edition,  revised  and  enlarged.  41 6  pages, 
183  illustrations 2.50 

Alternating  Currents.  An  Analytical  and  Graph- 
ical Treatment  for  Students  and  Engineers.  By  Frederick 
Bedell,  Ph.D.,  and  Albert  C.  Crehore,  Ph.D.  Second 
edition.  325  pages,  1 12  illustrations 2.50 


Publications  of  the  W.   J.   JOHNSTON  COMPANY. 

Gerard's  Electricity.  With  chapters  by  Dr.  Louis 
Duncan,  C.  P.  Steinmetz,  A.  E.  Kennelly  and  Dr.  Gary 
T.  Hutchinson.  Translated  under  the  direction  of  Dr. 
Louis  Duncan $2.50 

The  Theory  and  Calculation  of  Alternat- 
ing-Current Phenomena.  By  Charles  Proteus 
Steinmetz 2.50 

Central  Station  Bookkeeping.  With  Suggested 
Forms.  By  H.  A.  Foster 2.50 

Continuous  Current  Dynamos  and  Motors. 

An  Elementary  Treatise  for  Students.      By  Frank  P. 
Cox,  B.  S.     271  pages,  83  illustrations 2.00 

Electricity  at  the  Paris  Exposition  of 
188«J.  By  Carl  Hering.  250  pages,  62  illustrations.  2.00 

Electric  Lighting1  Specifications  for  the  use  of 

Engineers  and  Architects.     Second  edition,  entirely  re- 
written.    By  E.  A.  Merrill.     213  pages 1.50 

The  Quadruplex.-  By  Wm.  Maver,  Jr.,  and  Minor 
M.  Davis.  With  Chapters  on  Dynamo -Electric  Machines 
in  Relation  to  the  Quadruplex,  Telegraph  Repeaters,  the 
Wheatstone  Automatic  Telegraph,  etc,  126  pages,  63 
illustrations . . , 1.50 

The  Elements  of  Static  Electricity,  with  Full 
Descriptions  of  the  Holtz  and  Topler  Machines.  By 
Philip  Atkinson,  Ph.D.  Second  edition.  228  pages, 
64  illustrations 1.50 

Lightning  Flashes.  A  Volume  of  Short,  Bright 
and  Crisp  Electrical  Stories  and  Sketches.  160  pages, 
copiously  illustrated 1.50 

A  Practical  Treatise  on  Lightning  Pro- 
tection.- By  H.W. Spang.  180 pages,  28 illustrations,  1.50 


Publications  of  the  W.   J.   JOHNSTON  COMPANY 

Electric  Street  Railways.  By  E.  J.  Houston, 
Ph.D.  and  A.  E.  Kennelly,  D.Sc.  (Electro-Technical 
Series) f!.oo 

Electric  Telephony.  By  E.  J.  Houston,  Ph.D. 
and  A.  E.  Kennelly,  D.Sc.  (Electro-Technical  Series). .  i.oo 

Electric  Telegraphy.  By  E.  J.  Houston,  Ph.D. 
and  A.  E.  Kennelly,  D.Sc.  (Electro-Technical  Series). .  i.oo 

Alternating  Currents  of  Electricity.    Their 

Generation,  Measurement,  Distribution  and  Application. 
Authorized  American  Edition.  By  Gisbert  Kapp.  164 
pages,  37  illustrations  and  two  plates i.oo 

Recent    Progress    in   Electric    Railways. 

Being  a  Summary  of  Current  Advance  in  Electric  Rail- 
way Construction,  Operation,  Systems,  Machinery, 
Appliances,  etc.  Compiled  by  Carl  Hering.  386 
pages,  1 10  illustrations I.oo 

Original  Papers  on  Dynamo  Machinery 
and  Allied  Subjects,  Authorized  American 
Edition.  By  John  Hopkinson,  F.R.S.  249  pages,  90 
illustrations 1 .00 

Davis'  Standard  Tables  for  Electric  Wire- 
men.  With  Instructions  for  Wiremen  and  Linemen, 
Rules  for  Safe  Wiring  and  Useful  Formulae  and  Data. 
Fourth  edition.  Revised  by  W.  D.  Weaver i.oo 

Universal  Wiring  Computer,  for  Determining 
the  Sizes  of  Wires  for  Incandescent  Electric  Lamp  Leads, 
and  for  Distribution  in  General  Without  Calculation, 
with  Some  Notes  on  Wiring  and  a  Set  of  Auxiliary 
Tables.  By  Carl  Hering.  44  pages I.oo 


Publications  of  the  W.  J.   JOHNSTON  COMPANY. 

Electricity  and  Magnetism.  Being  a  Series  of 
Advanced  Primers.  By  Edwin  J.  Houston,  Ph.D.  306 
pages,  1 16  illustrations $1.00 

Electrical  Measurements  and  Other  Ad- 
vanced Primers  of  Electricity.  By  Edwin 
J.  Houston,  Ph.D.  429  pages,  169  illustrations i.oo 

The  Electrical  Transmission  of  Intelli- 
gence and  Other  Advanced  Primers  of 
Electricity.  By  Edwin  J.  Houston,  Ph.D.  330 
pages,  88  illustrations i.oo 

Electricity  One  Hundred  Years  Ago  and 
To-day.  By  Edwin  J.  Houston,  Ph.D.  179  pages, 
illustrated  i.oo 

Alternating   Electric   Currents.      By  E.  J. 

Houston,  Ph.D.  and  A.  E.  Kennelly,  D.Sc.  (Electro- 
Technical  Series) i.oo 

Electric  Heating.  By  E.  J.  Houston,  Ph.D.  and 
A.  E.  Kennelly,  D.Sc.  (Electro-Technical  Series) i.oo 

Electromagnetism.  By  E.  J.  Houston,  Ph.D.  and 
A.  E.  Kennelly,  D.Sc.  (Electro-Technical  Series) I.oo 

Electro-Therapeutics.  By  E.  J.  Houston,  Ph.D. 
and  A.  E.  Kennelly,'  D.Sc.  (Electro-Technical  Series). .  i.oo 

Electric  Arc  Lighting.  By  E.  J.  Houston,  Ph.D. 
and  A.  E.  Kennelly,  D.Sc.  (Electro-Technical  Series). .  i.oo 

Electric  Incandescent  Lighting.     By  E.  J. 

Houston,  Ph.D.  and  A.  E.  Kennelly,  D.Sc.  (Electro- 
Technical  Series) i.oo 

Electric  Motors.  By  E.  J.  Houston,  Th.D.  and  A. 
E.  Kennelly,  D.Sc.  (Electro-Technical  Series) i.oo 


Publications  of  the  W.   J.   JOHNSTON  COMPANY. 

Experiments  With  Alternating  Currents 
of  High  Potential  and  High  Frequency. 

By  Nikola  Tesla.     146  pages,  30  illustrations $1.00 

Lectures  on  the  Electro-Magnet.  Authorized 
American  Edition.  By  Prof.  Silvanus  P.  Thompson. 
287  pages,  75  illustrations i.oo 

Dynamo  and  Motor  Building  for  Amateurs. 

With  Working  Drawings.     By  Lieutenant  C.  D.  Park- 
hurst I.oo 

Reference  Book  of  Tables  and  Formulae 
for  Electric  Street  Kail  way  Engineers. 

By  E.  A.  Merrill i.oo 

Practical    Information   for    Telephonists. 

By  T.  D.  Lockwood.     192  pages i.oo 

Wheeler's  Chart  of  Wire  Gauges. i.oo 

A  Practical  Treatise  on  Lightning  Con- 
ductors. By  H.W.  Spang.  48  pages,  10  illustrations.  .75 

Proceedings  of  the  National  Conference  of 
Electricians.  300  pages,  23  illustrations. 75 

Wired  Love  ;  A  Romance  of  Dots  and  Dashes.  256 
Pages 75 

Tables  of  Equivalents  of  Units  of  Measure- 
ment. By  Carl  Hering 50 

Copies  of  any  of  the  above  books  or  of  any  other  electrical  book 
published,  will  be  sent  by  mail,  POSTAGE  PREPAID,  to  any  address 
in  the  world  on  receipt  of  price. 


THE  W.  J.  JOHNSTON  COMPANY, 

253  BROADWAY,  NEW  YORK. 


THE  PIONEER  ELECTRICAL  JOURNAL  OF  AMERICA, 


Read  Wherever  the  English  Language  is  Spoken 


The  Electrical  "World 

is  the  largest,  most  handsomely  illustrated,  and  most  widely 
circulated  electrical  journal  in  the  world. 

It  should  be  read  not  only  by  every  ambitious  electrician 
anxious  to  rise  in  his  profession,  but  by  every  intelligent  Ameri- 
can. 

It  is  noted  for  its  ability,  enterprise,  independence  and 
honesty.  For  thoroughness,  candor  and  progressive  spirit  it 
stands  in  the  foremost  rank  of  special  journalism. 

Always  abreast  of  the  times,  its  treatment  of  everything 
.relating  to  the  practical  and  scientific  development  of  electrical 
knowledge  is  comprehensive  and  authoritative.  Among  its 
many  features  is  a  weekly  Digest  of  Current  Technical  Electri- 
cal Literature,  which  gives  a  complete  resume  of  current  origi- 
nal contributions  to  electrical  literature  appearing  in  other 
journals  the  world  over. 


Subscription  {Ml«a*S^^^u-s-'}$3  a  Year. 

May  be  ordered  of  any  Newsdealer  at  10  cents  a  week. 


Cloth  Binders  for  THE  ELECTRICAL  WORLD  postpaid,  $1.00. 


The  W.  J.  Johnston  Company,  Publishers, 

253  BROADWAY,  NEW  YORK. 


YB  53660 


w 


53Fi»witiji 


% 


PftpPfftTY  OF 

^Ff,f  .,m       XNO^! 


^ 


M289307 


THE  UNIVERSITY  OF  CALIFORNIA  LIBRARY 


